Objective Previous work has linked high levels of belongingness needs to low well‐being, suggesting that high desire for social connection causes problems. Against that view, we hypothesized that problems stem especially from unmet belongingness needs. To examine this, discrepancies between belongingness needs and relationship satisfaction were measured. Method A total of 1,342 adolescents (Mage = 13.94 years, 48.6% boys) completed questionnaires about belongingness needs, relationship satisfaction, loneliness, depressive symptoms, and self‐esteem. A combination of polynomial regression analyses with response surface modeling examined the effects of both fulfilled and unmet belongingness needs on well‐being. Results Fulfilled belongingness needs did not affect adolescents' well‐being. However, larger discrepancies between high belongingness needs and low relationship satisfaction were related to higher loneliness, more depressive symptoms, and lower self‐esteem. Thus, well‐being was most strongly affected among adolescents reporting an unmet need to belong. Conclusions We add to the current knowledge by emphasizing that especially belongingness needs that exceed relationship satisfaction, regardless of the actual levels of both, contribute to actual health outcomes. Thus, high need to belong is not detrimental per se, but only in combination with low relationship satisfaction. Implications for clinical practice could be to prevent unmet belongingness needs to ultimately alleviate negative affect and self‐esteem.