I just started dating this girl two weeks ago and things

I just started dating this girl two weeks ago and things are going great. she's cute, charming, extremely hot, and best of all - she thinks the same of me. Last night I met with my best friend (girl) to watch a movie. We ended up having sex. I will still keep dating the girl i was dating. I don't feel guilty. At all. I feel guilty for not feeling guilty.