["Journal of Personality, EarlyView. ", "\nABSTRACT\n\nObjective\nAs social norms and relationship dynamics evolve, it is important to examine how transitions from singlehood to partnership, cohabitation, and marriage relate to well‐being.\n\n\nMethod\nUsing data from two large panel studies in the UK and Germany (1984–2019), we identified N = 27,459 individuals who reported being single and living alone at least once. Analyses focused on a subset (N = 1103; Mage = 38.35, SDage = 13.87; 43.8% women) who later entered a relationship and moved in with a partner.\n\n\nResults\nLife satisfaction increased over the short to medium term after cohabitation across most socio‐demographic groups. The increase peaked in the year of moving in (Δ ≈ 0.48 SD) and remained above pre‐transition levels for the 2 subsequent years analyzed. Those who had found a partner one year before had already achieved significantly higher life satisfaction, while cohabitation showed no additional effect. Marriage showed a short‐lived additional effect in the early 1990s, but not more recently. Lower‐income individuals experienced a stronger post‐peak decline.\n\n\nConclusion\nFindings suggest that well‐being increases are more closely aligned with relationship formation than with cohabitation or marriage. Among participants already in a relationship, increases in well‐being were observed prior to cohabitation, suggesting anticipatory effects.\n\n"]