Need your advice

Ok so i don’t normally ask for help on these things but i’m really really confused.

Me and my girlfriend have been going out for 2 1/2 years and i found recently that she had kissed a guy a while ago. I also found messages between her and him saying i was long gone and that they could have the house to themselves if he came over. Now he lives in london ( we live in perth (australia)  and she has gone to melbourne for 4 months. She had lost her job here and her car and has stuffed up her life a lot so she went there to get a job, save some money and come back so we can move out. I kow how bad that sounds (and it is) but i love her and i believe she still loves me, she wants me to forgive her. I’m really torn, i believe that if you love someone then you at least give them a second chance yet if she loved me then she wouldnt have done it. I’m not making excuses but i am 26 and still live with my P’s, i have just finished uni and got a casual full time job which means i cant risk moving out. I have put it off for so long, my lifestyle is crap and i smoke pot everynight which she doesn’t know about. i think it i could be different if i lived better and the person i am really does rub off onto her. I don’t think i’m the happiest person to be around and if i changed how i live i feel as though things would be better and could work. I’ve told her that we need time and that’s all i can promise. It’s so hard because i want to believe that she was lost and confused (which i think is possible, i couldnt support her and she has moved in and out with her parents who hate me). It all sounds messed up i know, i have read some messages and i agree that there was little trust and that the relationships was not the best, She really is trying, i beleiev she is sorry but what can i do? I know my family and friends will be annoyed with me but i also know this is my life. At the moment i hate her for what she did and i hate myself for not seeing it coming, i promised myself i would change a long time ago so this didn’t happen again. Is it too late to change and make it work?

Any advice would help, any thoughts are welcome.