I've been dating this guy on and off for months and I'm still really into him and my bf asked me if they could "hang", should I not feel like my gf is betraying me and just move on, is this how bf's treat eachother? I feel like shit, i'm sad and I'm way pissed at my gf, is that normal HELP!

as for any advice, I would say talk to her about her intentions with him, let her know that you are still not over him. Every friendship is different.
As a rule my girl besties know to not date any of our exes, but that's something we all talked about and concluded. If you need to do that with your friend, then go for it.