right now im a mess and not sure what i should do or what to expect in writing this but I need to get it out

2 nights ago I was going through my girlfriends phone because she was showing me something and then I decided to just be nosy and she kept trying to get her phone so it made me more curious. come to find out she had snapchat on her phone which we agreed a long time ago to not have because it made me insecure. and, she was talking to a guy friend who she says is her gay friend (my opinion is that he is a bisexual)

before we ever decided to delete sc before she agreed to not talk to this person and deleted him, I found out a month later that she added him back and was chatting with him so then I did stupid stuff and added girls on my sc and got out of hand myself so we both agreed to delete snap chat. this was several months ago. she mentioned in passing one day that she was thinking of making a new one so she could see her family who lives 3 hours away, I told her no because it wasnt a good idea. this was weeks ago....now just a couple nights ago I find out she has had it for some weeks now and has been chatting with not just her family but her "gay" friend as well.
I'm really just tired of all this and I know that I'm mad and hurt right now at the moment and things might be better after awhile and this is just snapchat not a big deal to some people but should I really continue to keep giving her chances, I feel like a idiot right now for allowing this.

when I asked why she did this, she said that she told me she was going to and that I probably didnt hear her but I told her we wouldve had a more serious conversation if i heard of her really seriously considering having a sc again. she said she thought we were past all that and have grown so she thought it was ok....

I had so many plans now that she was done with school for semester for christmas dates and gifts but now i just feel like a idiot and really dont want to get her anything at all. i already pay the bills and take care of her while she goes to school to find out im being betrayed....

please let me know what everyone thinks and sorry about my typing