Im really confused and need help?

So like me and my girlfriend went to a party and we both got drunk then i saw her talking to this guy. long story short the guy talked to me and he said that hes sorry about what happened (which is flirting) he said they were just drunk and not to worry bcs nothings gonna happen. then my girlfriend talked to me and she said not to worry because she'll never do it again. I love my girlfriend and she loves me too but why am i getting this feeling? is this normal?