We know that being friends with other couples increases closeness in your own relationship (read more about this here). To see if these friendships also boost feelings of love, researchers had couples engage in a “fast friends” self-disclosure task during which they answered questions such as “What is the greatest accomplishment of your life?”. Couples answered questions either alone or with another couple, and then reported feelings of passionate love (e.g., “I will love my partner forever”). Though there were no changes in passionate love when couples disclosed by themselves, those who answered questions with another couple reported greater passionate love in their own relationships.
Welker, K. M., Baker, L., Padilla, A., Holmes, H., Aron, A., & Slatcher, R. B. (2014). Effects of self‐disclosure and responsiveness between couples on passionate love within couples. Personal Relationships, 21(4), 692-708.