Should I say something or stay out of it?

There's this girl in my grade, and we aren't friends. She's had this boyfriend for over a year and four months now, and she has him completely whipped. I have witnessed her literally snap her fingers, and he came running to her. Basically, she treats him like absolute sh*t but claims to love him, and he is madly in love with her. Everyone in my grade knows this and smirks about it behind their backs.

Last night, I was told that the girl was at some party without her boyfriend, and she hooked up with a sophomore. She then asked the sophomore if she could give him a bl*wjob, but the sophomore said "No, think about what you're doing." But still, she hooked up with this other guy. The girl's boyfriend is completely unaware of this.

I'm debating on whether or not I should say something to the girl's boyfriend. Him and I used to be friends around two years ago, but we haven't spoken in a long time (he's been spending every waking minute on his girlfriend). As I said, I'm not friends with the girlfriend either, I actually quite dislike her. I don't know if the boyfriend would even believe me, he's so obsessed with his girlfriend. Should I say something to him or just mind my own business?