What should I do with this guy?

Your letting your friend decide for you? Sorry thats a no go. If you like him you don’t need her approval to go out with him, friends typically support you in these type of things. In her case however she has no reason to say no, she is a lesbian according to what you said and she shouldn’t care unless the guy is some kind of player. I really don’t get why she doesn’t want you with him and you said she doesn’t even like him. Thats a bit odd of her, if shes a close friend of yours then there are several things to weigh in, go out with him and lose her or the complete opposite.

Honestly though I would try to get her to understand. In a sense she is preventing you of having a wonderful experience with a guy you like and thats not right. If you want you can try and talk to her about it and see why she doesn’t want you with him. Get her to talk about her perspective and then you can voice out your own. In the end though the ball is in your court.