Everybody has been unnecessarily harsh here, I think. Desire discrepancy and libido mismatches happen for all sorts of reasons. Just because you don’t have sex doesn’t mean she’s not your girlfriend, and I’m glad you see that. It sounds like you’re in sort of a queerplatonic relationship. She’s not just a friend, like some people are trying to say.

I hate it when people think a relationship is basically disposable because one person wants to fuck and the other one doesn’t. They aren’t to everyone, it depends on what both partners decide.

The real issue is her complaining to you about not getting laid. It seems discourteous of her, since she knows how you feel. I get that she was frustrated and venting, too, but she should have thought about who she was venting to. If I were you, I would have a sit down with her and let her know that hearing about her complain about desiring more sex and not getting it is difficult for you, since you would love to have sex with her. I would then ask her not to talk about sex with other partners or wanting sex with other partners with me. It does nothing to help your relationship except make you think like a scorekeeper.