Cheater advice

I'm from a small Texas town where everyone knows everyone! Anyways, there's this guy I messed around when ONCE when I was a senior in high school, probably 17, and I'm now 21. He had a long term girl friend, whom I know, and I have a long term boyfriend who recently moved in with me, whom he knows! His girl friend is such a sweet girl, and we go to the same church, but we are not friends. He just texted me, and added me on snapchat (which I've made a new one because he used to send inappropriate snaps recently) and I know he's only trying to "booty call me" although I have no interest what so ever seeing as I'm HAPPILY taken. And he also snaps/texts my best friend in a sexual way.... So my question is, should I tell his girl friend or leave it alone. I know for a fact it will look like I'm causing drama which I do not wish to do. I just hate to see a sweet girl be with a crummy guy.