This is absolute nonsense. Even in states where gay marriage is prohibited, there are many gay couples who have lived together for decades and consider themselves to be “married” even if the state doesn’t. They’re no more likely to break up than they would be with an official marriage license.
Actually, gay relationships are usually very different than straight relationships in fundamental ways. Importantly, they do not have the same concept of exclusivity with one’s partner. This is not controversial and not debated. So to compare the relationships is kinda silly.
Furthermore, sure, those relationships *can* end. But even when they do, the gay people will just find new partners, or engage in sexual activity outside of relationships. There is no way to “become straight again” because homosexuality is biological.
That is a nice opinion. I don’t know why you declare it though as if undisputed fact. It is in no way known that homosexuality is biological in the way you mean (I think the better word for what you mean is congenital.)