A study reported, in the 80's, that unmarried cohabitation prior to marriage was associated with "significantly" lower marital satisfaction, but did not report an effect size. They also reported that the duration of unmarried cohabitation was unrelated to marital satisfaction(DeMaris and Leslie, 1984). A later study by the same lead author from the 90's reported that unmarried cohabitation predicted later divorce after controlling for time in union (DeMaris and Rao, 1992), which I include because time in union could be a confounding factor and I could not find direct evidence.
Wydick (2007) gave a game theoretic account of why unmarried cohabitation may lead to relatively decreased marital satisfaction which I am not qualified to evaluate, but the paper cites a number of empirical studies that support DeMaris' older thesis, so this paper may also be of some interest.
Not to speculate, but this is subjectively surprising to me. When I began the literature search, I was confident the idea was nonsense, and yet here we are.
- DeMaris, A., & Leslie, G. R. (1984). Cohabitation with the future spouse: Its influence upon marital satisfaction and communication. Journal of Marriage and the Family, 77-84.
- DeMaris, A., & Rao, K. V. (1992). Premarital cohabitation and subsequent marital stability in the United States: A reassessment. Journal of Marriage and the Family, 178-190.
- Wydick, B. (2007). Grandma was right: Why cohabitation undermines relational satisfaction, but is increasing anyway. Kyklos, 60(4), 617-645.