When two couples interact in an intense, self-disclosing fashion, rapid expansion of the self may be especially strong after the initial exhilaration of a new relationship starts to fade. Take, for example, relationship partners who have been dating for a year and have become more and more accustomed to each other as their relationship has progressed. The two people, once very fresh and exciting to each other, seem less and less novel and self-expansion slows or comes to a halt. At this point, people may become bored and dissatisfied in their relationship (Aron & Aron, 1986). For long-term couples, intense self-disclosure with another couple may be sufficiently novel and arousing enough to lead to increased positive affect and, in turn, heightened feelings of closeness toward one’s partner..."
"When Harry and Sally Met Dick and Jane: Creating Closeness between Couples"
"...The first link in this proposed meeting another couple-->positive affect-->relationship closeness chain of associations is suggested in series of two daily experience sampling studies conducted by Larson and colleagues (Larson & Bradney, 1988; Larson, Mannell, & Zuzanek, 1986). In these studies, participants reported their highest levels of positive affect when they were engaging in activities with their spouses and friends together, compared to activities alone, with spouse only or with friends only. These findings provide preliminary evidence that increases in positive affect may be one mechanism through which friendships with other couples may lead to enhanced closeness within couples.