Should i forgive her?

I dated this guy and i broke up with him cause there was to much drama going on.But over the summer my best friend dated him and didnt tell me and on the 1st week of school this guy told me they were dating.So i stoped talking to her cause i was mad she didnt tell me then she came up to and said " Hey missy dont be mad at me i broke up with him a few days ago and the only reson i dated him was cause my friend said yes for me" but she said it in a nice way and i was like okay then one of my friends were like "you still mad at her for not telling you" and i was like "no she told me she broke up with him a few days ago" and he was like "thats messed up" and i wwas like "what" and hes like "they didnt break up, there were holding hands at lunch". and we been best friends for 4 years and i dont kno it i should for-give her or just forget her? what do you think i should do?