is my girlfriend cheating?

[Chris]

i need some advice please.i know it may seem obvious but i am just having a problem believing it.my girlfriend and i met a year ago and we hit it off real fast.it was an online relationship.she invited some guys and girls to her 19th birthday party.i do get a little jealous because i don't really know what's going on.she told me the guys were just friends and i had nothing to worry about.she told me the guys were taken and that her mom was going to be there.she still lives at home so i was starting to feel better.well i have her password to facebook .i went on there to copy a picture of hers and i see that on jan.2 she is in a relationship.there were comments on it between her and her mom.she asked how the relationship is going.she said we are so happy and we can't wait to see each other.so i went further into it to see who it was.i read a conversation between her and a friend the friend asked if she felt the same way about david as she does about carlos and she said yes.well david was one of the so called friend that was coming to the party and i really believed her this whole time.she told me loved me and she would never hurt me and 3 weeks later i see this.now i don't know if they met up but it's possible so i can't jump to any conclusions but it's pretty clear to me that she lied.david is not with the girl that she said he was with because i checked her profile and she is with another guy.all this time she has convinced me that i was the only one even to this day she says i love you.if she makes up some excuse should i believe her and just let it go until i have more proof or should i just say goodbye.if she is seeing him then she's cheating on both of us.i really need to know what to do about this
there's one thing i forgot to mention.on the 27th of last month i broke up with her because i thought she was trying to cheat with another guy.turned out he was just a friend and i had proof he was.she told me how bad it hurt and it would be hard to trust me again.but she is only giving me one more chance.then a week later she is in a relationship.is that still considered cheating even though i ended it for a stupid reason .did i just hang myself for this one,i kinda feel like i screwed up.

[Krissy]

Say goodbye, seeing that relationship status on her Facebook is all the proof you need. There are plenty of fish in the sea!

Good luck

[Ilas]

Tell her, we are done and you can date david now without lying to me. F*ck you b*tch.