GAGNON: WHY HOMOSEXUAL UNIONS ARE WRONG
If you're still processing this issue I would invite you to read Robert Gagnon's essay which is really a nice little summary of his work in this area. This is from the beginning of the article: Advocates of homosexual practice often argue that “gay marriage,” or at least homosexual civil unions, will reduce promiscuity and promote fidelity among homosexual persons. Such an argument overlooks two key points...

First, legal and ecclesiastical embrace of homosexual unions is more likely to undermine the institution of marriage and produce other negative effects than it is to make fidelity and longevity the norm for homosexual unions. We will come back to this later.

Second, and even more importantly, homosexual unions are not wrong primarily because of their disproportionately high incidence of promiscuity (especially among males) and breakups (especially among females). They are wrong because “gay marriage” is a contradiction in terms. As with consensual adult incest and polyamory, considerations of commitment and fidelity factor only after certain structural prerequisites are met.