The aim of this study was to examine intrapersonal (actor) and interpersonal (partner) associations between attachment, assessed by the Adult Attachment Interview, and satisfaction with the relationship, as well as to establish the possibility of the mediatory effect of supportive, delegated, and common dyadic coping on the aforementioned associations. A dyadic approach has been introduced, using the actor–partner interdependence mediation model and data from 114 heterosexual couples, aged 26 to 60. It has been shown that one’s own secure attachment can be perceived as the predictor of one’s own relationship satisfaction in women and men and the predictor of a partner’s relationship satisfaction in men. The findings support the partially mediating role of dyadic coping in the association between attachment and relationship satisfaction and are a significant contribution to the issue of dyadic coping in general. Adults’ secure representations of their childhood experiences may be effective in using their partners as a secure base and also in serving as a secure base themselves, but it is not the sole influence on the quality of the couple’s experience together. The we-ness phenomenon and resulting clinical implications were discussed.