Vulnerable self-disclosure co-develops in adolescent friendships: Developmental foundations of emotional intimacy.

This study examines the development of vulnerable self-disclosure in supportive interactions from ages 13 to 29. A diverse community sample (N = 184; 85 boys 99 girls; 58% white, 29% Black, 13% other identity groups) participated in annual observed interactions with close friends and romantic partners. Participants were observed as they sought and provided support to their best friends each year from age 13 to 18, and as they sought support from their romantic partners from age 19 to 29. Random intercept cross-lagged panel models were used to parse markers of within-individual change in vulnerable self-disclosure observed annually across ages 13 to 18. A follow-up regression model also investigated cascading associations from vulnerable self-disclosure in adolescent friendships to vulnerable self-disclosure in adult romantic relationships. When adolescents sought support, they demonstrated greater-than-expected increases in self-disclosure each year when their best friends demonstrated relatively high self-disclosure. For girls in this sample, when providing support, they demonstrated greater-than-expected decreases in self-disclosure each year when their best friends demonstrated relatively high self-disclosure. Adolescents whose friends disclosed highly to them also tended to express more vulnerability with romantic partners in adulthood. Post-hoc analyses investigate the role of friendship stability and gender as potential moderators of self-disclosure development. The best friendship, a key source of emotional support, serves as a foundational context for learning appropriate use of vulnerable self-disclosure when seeking and providing emotional support, which persists across time and relationships.