Quantitative data on the length of gay/lesbian relationships is much harder to find, and not as numerous as data from those studies addressing heterosexual couples who are married. This is largely due to the fact that people in gay/lesbian relationships (in the U.$. at least) cannot legally marry, which means the government can't keep that same statistics on us as they do on heterosexual couples. In addition, a lot of the "information" found during a simple Google search will produce results from anti-gay, anti-marriage, and even pro-gay-marriage groups pushing for certain legislation. Many so-called studies by these groups give a single number for the length of gay/lesbian relationships without credible citations.
With that being said, there definitely are statistics about queer relationships and heterosexual relationships that might be of some help:
- Another Rad Reffer found this study, which is somewhat dated, but still very good information.
- "Relationship Outcomes and Their Predictors: Longitudinal Evidence from Heterosexual Married, Gay Cohabiting, and Lesbian Cohabiting Couples" by Lawrence A. Kurdek (Journal of Marriage and the Family, Vol. 60, No. 3 (Aug., 1998), pp. 553-568) is a study where the author wanted to find out, "if members of married couples differed from those of either gay couples or lesbian couples on five dimensions of relationship quality, two relationship outcomes ([one of which being] relationship dissolution over 5 years), and the link between each dimension of relationship quality and each relationship outcome." The results from this study show that, among other things, relative to married couples, both gay and lesbian partners reported more frequent relationship dissolution.
- In the article "What Do We Know About Gay and Lesbian Couples?" by Lawrence A. Kurdek (Current Directions in Psychological Science Volume 14 Page 251 - October 2005), the author states that, "although rates of dissolution did not differ for either gay couples versus lesbian couples or for gay and lesbian couples versus cohabiting heterosexual couples, both gay and lesbian couples were more likely to dissolve their relationships than married heterosexual couples were." Furthermore, the author states that because persons in a marriage relationship face "social, religious, and legal barriers to leaving their relationships," cohabitating heterosexuals and gays and lesbians in relationships do not, making it easier to dissolve a relationship. The fact that for the most part, gay and lesbian couples do not have children, is one less barrier to dissolution that gay and lesbian couples face.