My gilfirend's and I; relationship is complicated and possibility a break up?

I would either talk to her about how your feeling about all this or just break up with her...If she is just going to go back to him then you don't deserve to be treated like this. I'm sorry this is happening to you hun. It isn't fun being in a situation like this...I've been through things like this and the best thing to do is either talk it through or just let go. Sorry. :/ Hope all goes well!