I would unfriend the guy with a message on how hurtful he was to post on your page the things he did. I would talk to your GF and tell her why you unfriended her beau. She may know about him being that way, but not want to choose, or she may think he will change and become more accepting once he knows you better. Technically, I suppose it's really his problem, not hers, but if she wants to see you and be friends with you, make it clear he is not welcome to tag along as you are uncomfortable.
I guess I would not make my friend choose between me and her guy, because once she does realize how much of an asshole he really is, she will need you to help her pick up the pieces again. If the relationship is worth it to you.
Don't be afraid, it's only love!