How should I feel about my girlfriend going to a dance without letting me know or asking me if I minded?

Question

So here's what happened..My girlfriend of 5 months asked me to go to a school dance like 5 days before the day of the dance. I said i didnt really want to go to it because i dont really like dances. She said she didnt want to go if i dont go because she'd be dancing with other guys. I thought that was really cool of her. I asked her if she wanted to hangout on the day of the dance instead and she said sure, although i know she did want to go to the dance. The day of the dance comes around and I havnt heard from her all day (no classes with her shes a year younger). So I get home and I'm waiting around for her call..she never did. I go on msn and the first thing someone says to me is "yo I was pimpin your broad at the dance tonight"..I was confused..and then my girlfriend signs in and says oh hey sorry i changed my mind and went to the dance..and when i said we had plans she said she had forgotten. I was really hurt and lost some trust, and get a sick feeling everytime I think about it.

Answer 1

dump her. any girl that breaks plans without letting you know and then goes and dances with other guy at the dance is no girl you want to be with. i'm sure she was mad that you didn't want to go but she should have discussed it with you first.
find a new girl that respects you and treats you well enough to let you know that she is cancelling instead of standing you up.

Answer 2

she should of been honest with you and said she really wanted to go to the dance instead she went without telling you... she pretty much lied about it.. shes not trustworthy... and u2 seem so young.. im sure u will find a new girlfriend by the weeks end... either u gotta go to the dance and dance or get a new girl...