Is he obsessed or something?

I used to like him, a lot. That's kind of fading away now (thankfully). We used to be FWB which was a huge mistake as i ended up wanting more, as i said, stupid. Anyway, he has a girlfriend who he's been with over a year but the way he acts you'd think he's single. He's a HUGE flirt, and i don't just mean being friendly, he talks about ual things pretty graphically, to me anyway. When he's out (i've been told) he picks up women and spends the night with them when his girlfriends not around. He wants to sleep with me and has also said the same thing to another girl i know. If i hug him, just as friends are supposed to do, he'll comment on being able to feel my against him. Why is he so obsessed with ? Now that i know he's like that my feelings for him have become much less intense.