Girl cheated on her boyfriend - with me and i didnt know it till today. She kept telling me they were broken up and all that stuff, then i find out from a friend, all the times we did stuff, she was with the other guy at that time. Should i be pissed? She says she is staying with him and is acting towards me like she just chose to be with him today, when they had been going out for weeks. Im not sure if i should go off or just next her? Any advice?