I can't really speak for lesbian relationships, but I've definitely witnessed some situations where double the testosterone, double the male-insecurity, and double the male sex drive led to some extremely angry and violent relationships. I know of one couple that had knock-down drag-out fist fights at least once a month. They swore that they were in love, but I don't see how that could possibly be the case. Looked to me like they were stuck in a co-dependent nightmare. But whatever. It's not my place to judge them. (I
did judge, mind you, it's just not my place.

)
I don't think that same-sex relationships are any more or less prone to dysfunction than straight relationships are. I think it's too much of a blanket statement to make either way. Each couple is different, and has to be judged solely on itself.
Just my two cents.