Feeling betrayed by her isn't just going to go away. You have a solid reason to feel hurt. I have no idea if I could ever feel comfortable in a relationship where I had been betrayed before.

Your girlfriend needs to be bending over backwards to prove now that she's commited to you. She committed a relationship sin and it's understandable that you feel hurt. If she's going to apologize, she needs to be making an effort to understand how you feel. At this point, I do not think that it is out of line to ask her not to hang out with guy friends in situations that you are not comfortable with.

It's extremely sad that you had gotten over jealousy issues just to be thrust in a position that validates them.