How do i?

How do I keep a really good friend close to me, with out his girlfriend in the way. She already don't want us talking, but I have liked him for a long time and I want to stay friends with him.

You need to set things straight with her. She might have a relationship with him but she doesn't need to isolate him from his friends. If you're not hitting on him or showing romantic interest, there's no need for her to be jealous. So she's the one you need to talk to, and be sorta friendly about it. See if you can get her to go somewhere with you, get her guard down. Try not to make a conflict about it because you could make him mad and her feel worse about you being around. Or, you could talk to him, and tell him to talk to her about accepting you.
But either way, she should not be keeping him from any of his friends. She has no right to do it.