I've known many same-sex couples in my life. And I have to say that the ones I've known have had the healthiest, longest lasting relationships I've ever seen. I'm sure that there must be as many disfunctional same-sex relationships proportionately as hetero relationships but that has not been my own personal experience.

The majority of my friends and family have been divorced and remarried. In fact I can only count about 20 marriages that I know of that have lasted 20 years or longer. On the other hand, of the 20ish same sex couples that I've known, all but one have remained with the same partner. Of those relationships, I know that two have lost their partners in death, and do not appear to be looking for a new mate. And one of those people seems to have a goal of sleeping with as many people as possible.