I think you are right about lesbian relationships lasting longer than gay mens’ but it still doesn’t make it right. There is more domestic abuse in lesbian relationships than the normal average. Women tend to be very jealous not only of other women but the fear that they are going to lose their partner to a man so its a double whammy.
I think jealousy may be one cause, but I also think lesbians have much more stressful lives than heterosexual women. They may be alienated from their families, society in general doesn’t acknowledge their relationships with the same sort of validation heterosexual couples get, and they cannot have children without going to a good deal of trouble. Once they do have kids, the child is only considered as belonging to one parent unless they arrange an adoption to make them both legal parents. As their children grow up I’m sure they worry about their children a great deal. We take a lot of things for granted that lesbian couples cannot.
There are probably additional sex differences factoring into it, like women’s tendency to become very dependent on their partners, so while a man might leave if his female partner abuses him (again, the definition of abuse is often very wide, it’s said 1/4 to 1/3 of heterosexual relationships are abusive) he is more likely to get fed up and walk out, while a woman might be more likely to stay with her abusive partner.
Again, domestic abuse in some lesbian relationships doesn’t make lesbian relationships wrong in general.