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Human Development · Foundations

Relationships

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On this page 9 sections
  1. In 30 seconds
  2. Why this matters
  3. The college version
  4. Eli explains
  5. Worked example
  6. Key takeaway
  7. Quick check
  8. Study tools
  9. Sources & references

In 30 seconds

are the close bonds of friendship, partnership, and care that shape adult life — the bonds through which adults experience , a basic need in self-determination theory. This lesson covers how friendships change with , Sternberg's triangular theory of romantic love (, , ), how early attachment patterns echo in adult bonds, the forming-maintaining-ending life cycle of relationships, and why these bonds support development from early adulthood to old age.

Why this matters

Understanding relationships as a developmental topic changes how you read the people around you. A friend who disappears after becoming a parent is not flaky; friendships are reshaped by life transitions. A couple whose early excitement has cooled is not failing; love mixes passion, intimacy, and commitment in shifting proportions. And this is not abstract: supportive friendships in early adulthood predict psychological and physical health, and staying connected with others is linked to purpose and longevity in later life. This lesson gives you the vocabulary — friendship change, the love triangle, attachment echoes, the relationship life cycle — to see adult bonds as developing, like everything else.

The college version

The working definition: adult bonds in developmental terms

Developmental psychologists study adult relationships as the close bonds of friendship, partnership, and care that shape adult life. The idea of relatedness anchors the definition: self-determination theory holds that well-being depends on balancing three basic needs — autonomy, competence, and relatedness — and relationships are the channel through which relatedness flows (Ryan & Deci, 2000, cited in OpenStax Lifespan Development 12.3). A second anchor is the : Kahn and Antonucci describe the set of relationships that travels with a person through life, gaining and losing members over time (OpenStax 16.2). Within that moving convoy, three broad forms matter most for adults: friendships (chosen peers), partnerships (romantic bonds, with or without legal status), and care bonds (family and other ties built around looking after one another). These are the adult bonds this lesson examines; infant-caregiver attachment and family development each have their own lessons.

Friendship in adulthood: change tied to life transitions

Developmental researcher Jeffrey Arnett, reviewing the research on friendship development, concluded that friendships change over the course of emerging adulthood, and the changes are linked more closely to life transitions — starting college, beginning a career, entering or leaving a romantic relationship, becoming a parent — than to age itself (Arnett, 2015, cited in OpenStax 12.3). Two findings round out the picture. First, friendships deepen in early adulthood, gaining intimacy and trust; close, supportive friendships reduce loneliness and predict both psychological and physical health. Second, friendship networks expand in young adulthood, largely because friendships form in the settings of daily routine — school, work, and community — and then the overall social network gradually shrinks from early to later adulthood (Wrzus et al., cited in OpenStax 12.3 and 16.2). Original example: when Nadia moved from Detroit to Austin for a medical residency, her college group's weekly dinners became monthly calls, while two hospital coworkers became her daily support. Her friendships did not age; they reorganized around a transition.

Romantic love: Sternberg's triangle

Psychologist Robert Sternberg's (1986) proposes that love combines three components. Passion is the longing, excitement, and attraction toward another person. Intimacy is closeness: sharing, self-disclosure, and mutual understanding. Commitment is loyalty and reliability — the decision to keep spending time together (OpenStax 14.2). The components combine in different proportions, producing different kinds of love. , intimacy plus commitment without strong passion, appears in friendships and family bonds as well as long partnerships. , all three components together, is the fullest form. Research on young adults finds the most fulfilling romantic relationships are characterized by all three (Bauermeister et al., cited in OpenStax 12.5), and the components shift across the lifespan — passion and intimacy peak in early adulthood and ease slightly in middle adulthood without disappearing (OpenStax 14.2).

Attachment in adulthood: echoes of the first bonds

Attachment research began with infant-caregiver bonds, but Hazan and Shaver (1987) proposed that the security of that first bond continues to matter across the lifespan, including in adult romantic relationships (OpenStax 12.5). Adults with secure attachment tend to show better conflict resolution, more mutual caring and trust, and greater emotional closeness and satisfaction in their relationships. This is an echo, not a verdict: early patterns tilt the way people approach closeness, but adult relationships are shaped by many later experiences as well. Original example: Lena, who learned as a child that caregivers were dependable, finds it natural to ask her partner for support; Marco, who learned to expect care to be unreliable, tends to brace for disappointment. Neither is stuck; each is working from an early template. The full treatment of attachment belongs to its own lesson.

The relationship life cycle: forming, maintaining, ending

Adult relationships move through a rough life cycle. Forming: bonds begin in shared settings and transitions — the new job, the new city, the class, the club — because friendships and partnerships form where daily routines overlap (OpenStax 12.3). Maintaining: bonds are kept alive by deliberate effort — shared time, self-disclosure, trust, and the loyalty of commitment; the social convoy perspective notes that people who nurture existing relationships keep them in the convoy, and health guidance likewise emphasizes scheduling time to stay in touch (OpenStax 16.2; NIA). Ending: relationships end when needs go unmet; young adults most often end romantic relationships because a partner did not meet their need for connection or did not support their need for independence (OpenStax 12.5). Endings are normal turnover, not failures: throughout life people gain new relationships and end old ones (OpenStax 16.2). Original example: a neighborhood book club that formed around a shared stoop, thrived for six years of monthly meetings, and quietly dissolved when three members moved away — a complete, ordinary life cycle.

The honest note and the honest framing

Two honest statements close the lesson. The honest note: relationships take many forms. About half of young adults are single at any given time, and research treats singlehood as a common, developmentally normal state rather than a problem to fix (OpenStax 12.5). Companionate love flourishes in friendships, family bonds, and other non-romantic ties (OpenStax 14.2), and social networks are made of many relationship types, not just one (OpenStax 16.2). The honest framing: relationships are the scaffolding of adult development. Supportive friendships in early adulthood predict psychological and physical health (OpenStax 12.3); people who stay connected with others and engage in meaningful activities feel a sense of purpose and tend to live longer (NIA); and loneliness in later life is correlated with a range of health problems (OpenStax 16.2). Relationships are not decoration on adult life; they are its structure.

Eli, the EliExplains learning guide

Eli explains

The same idea, in plain words

Explain it like I’m 10

Adult relationships are the people you are close to — friends, partners, and family you keep near — and they change as your life changes. A friendship that survives a move looks different from one that survives a shared dorm. Romantic love is like a triangle with three sides: the spark (passion), the closeness (intimacy), and the staying (commitment). Strong romances usually have all three, but the amounts shift over time, and love built on closeness plus commitment is still love. The way you learned to trust as a child echoes in how you trust a partner later — an echo, not a life sentence. Relationships begin, need effort to last, and sometimes end; that is normal, not failure.

Picture it like this

Think of adult relationships as a shared garden. Some plants are perennials — a college friend who blooms every spring no matter how far apart you live. Some are annuals — a work friend who flourishes for one season and is gone when you change jobs. A romantic partnership is the centerpiece trellis: it needs the soil of trust, the sunlight of shared time, and the pruning of honest conversation. You do not plant it once and walk away. Gardens are kept; some gardens get replanted, and a well-kept garden changes shape over the years without ever being abandoned.

Where the picture stops working

Gardens are tended on a schedule, but relationships are not — a friendship can thrive for years with no planned maintenance day. Gardens have no wishes of their own, while people in relationships negotiate, choose, and sometimes walk away. And unlike soil, a relationship carries its history: how you learned to trust as a child shapes how the garden grows, so two identical gardens can grow very differently.

Worked example

Maya, 28, moved from Detroit to Austin for a software job just as three of her college friends became parents. Within a year, the group's weekly dinners became monthly video calls, and two friendships faded to birthday texts. Maya read the loss as a personal failure until she noticed what had replaced it: a running partner from work, a neighbor who became her emergency contact, and a weekly call with her college roommate that had actually grown deeper. The friendship research names exactly this pattern: friendships reorganize around life transitions — relocation, parenthood, a new career — deepening in some forms while other forms fade. Maya's convoy had not shrunk; it had reshaped around the transitions of her life.

Key takeaway

Adult relationships are the close bonds of friendship, partnership, and care that supply relatedness across the lifespan: they reorganize around life transitions, love mixes passion, intimacy, and commitment in shifting proportions, and these bonds are the scaffolding that supports health and development from early adulthood to old age.

Quick check

3 questions here, of 5 in this lesson’s practice set. Answers stay hidden until you check.

Question 1 of 3foundational

According to Sternberg's triangular theory of love, which three components combine to form love?

Choose an answer, then check it.
Question 2 of 3foundational

Hazan and Shaver proposed that attachment security, first studied in infant-caregiver bonds, also continues to matter in which setting?

Choose an answer, then check it.
Question 3 of 3intermediate

Nadia moved to a new city for a residency; her college friend group's weekly dinners became monthly calls, while two hospital coworkers became her daily support. Which developmental finding does this best illustrate?

Choose an answer, then check it.
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Practice this lesson
Study tools & related lessonsYou’ll learn to · Common mistakes · Easily confused · Key vocabulary · Related

You’ll learn to

  • Define adult relationships in developmental terms as the close bonds of friendship, partnership, and care that supply relatedness.
  • Explain how friendships change across life stages, identifying life transitions rather than age as the main driver.
  • Describe Sternberg's triangular theory of love, naming passion, intimacy, and commitment and the kinds of love their combinations form.
  • Explain how early attachment patterns echo in adult relationships, per Hazan and Shaver, without treating the echo as destiny.
  • Apply the forming-maintaining-ending life cycle to an original example of an adult relationship.
  • Analyze why relationships function as scaffolding for adult development across the lifespan.

Common mistakes

  • A friendship that fades must have failed.

    Friendships reorganize around life transitions: the weekly dinner that disappears can coexist with a call that deepens. Fading in one form is not failure of the bond (Arnett, via OpenStax 12.3).

  • When the excitement fades, the love is over.

    Sternberg's theory separates passion from intimacy and commitment: many long bonds keep intimacy and commitment strong while passion ebbs. That is companionate love, not the end of love (OpenStax 14.2).

  • Your childhood attachment pattern is your romantic destiny.

    Hazan and Shaver propose echoes, not verdicts: early patterns influence how adults approach closeness, but adult relationships are shaped by later experience too (OpenStax 12.5).

  • A relationship that ends was wasted.

    Endings are a normal part of the relationship life cycle. Young adults most often end relationships because a partner did not meet their need for connection or independence — information, not failure (OpenStax 12.5).

  • Being single in early adulthood signals a problem.

    At any given time about half of young adults are single, and the developmental evidence treats singlehood as common and normal, not as a deficit (OpenStax 12.5).

Easily confused

Passion vs. Intimacy

Passion is the excitement and attraction toward a person; intimacy is the closeness built from sharing and self-disclosure. A brief fling can burn with passion yet stay shallow on intimacy, while a long friendship can be deeply intimate with no passion at all.

Companionate love vs. Consummate love

Companionate love is intimacy plus commitment without strong passion; consummate love holds all three components. A long marriage often glides from consummate toward companionate as passion cools, without becoming loveless.

Forming a relationship vs. Maintaining a relationship

Forming rides on shared settings and transitions — the new job, the new city — while maintaining rides on deliberate effort such as scheduled calls, disclosure, and trust. NIA's advice to schedule time to stay in touch is maintenance, not formation.

Key vocabulary

adult relationships
The lasting bonds adults form with friends, romantic partners, and family or care figures; in developmental terms, the close bonds of friendship, partnership, and care that shape adult life.
relatedness
The sense of being connected to and cared about by others; one of three basic psychological needs in self-determination theory, alongside autonomy and competence.
life transitions
Major changes in roles or circumstances, such as starting college, taking a first job, or becoming a parent; friendship changes track these more than age.
social convoy
The set of relationships that travels with a person through life, gaining and losing members over time (Kahn and Antonucci).
triangular theory of love
Sternberg's model proposing that love combines three components — passion, intimacy, and commitment — in varying proportions.
passion
The component of love involving longing, excitement, and attraction toward another person.
intimacy
The component of love involving closeness, self-disclosure, and mutual understanding.
commitment
The component of love involving loyalty, reliability, and the decision to keep sustaining the bond.
companionate love
Love built from intimacy plus commitment, without strong passion; it also appears in friendships and family bonds.
consummate love
Love that combines all three components — passion, intimacy, and commitment — together.

Sources & references

  1. Lifespan Development, Section 12.3: Relationships with Friends and Family in Early Adulthood (OpenStax) — OpenStax, Rice University
  2. Lifespan Development, Section 12.5: Finding Love, Intimacy, and Romance in Early Adulthood (OpenStax) — OpenStax, Rice University
  3. Lifespan Development, Section 14.2: Contexts: Love and Romance in Middle Adulthood (OpenStax) — OpenStax, Rice University
  4. Lifespan Development, Section 16.2: Contexts: Family, Friendships, Romantic Relationships, and Social Communities in Late Adulthood (OpenStax) — OpenStax, Rice University
  5. Loneliness and Social Isolation — Tips for Staying Connected (National Institute on Aging) — National Institute on Aging (NIH)

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Researched 2026-08-22

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