Hello christopher.piercy@hotmai,
Your partner should have used protection, or at the least she should have informed you that she broke that agreement. Well I guess she did, but I don't know whether she did so before having sex again with you. Okay, so that was one event. Now she has unprotected sex with another fella, then has sex with you without informing you. Not cool. I don't know whether cheating is the right word, but she definitely violated your trust. It is okay for you to feel crappy about this. You were done wrong.
Just some thoughts,
Kevin T.