I like this more than i thought. and how do i explain it to my girlfriend now?

Weekend with friends, dinner, laughter and a few drinks. some of them talk about their boyfriends and laugh when i tell them about things that happen to me with my girlfriend. what i least expect is that one of my friends enters my room tries to kiss me and wants us to fuck. and why not try it? my girlfriend is not here to see me and no one will tell her.