My guy friend is pushing me away and I don't know why... Ideas?

Okay, I like this guy who’s been with fifteen girls. I’m seeing passed that and I still like him. He’s admitted to be a sex addict or in his words “addicted to women and sex.” I’m really confused by him. He was hanging out with my brother and his friend a few days ago and he said to my brother that he didn’t want me liking him because he is a guy I shouldn’t be “mixing with.” He also says that I’m a really nice, sweet girl. He has said this to me via text as well, and on the phone he said to me that he isn’t a guy I should like because he “hurts girls.” I told him about a date I was going on and he seemed upset. He always seems bothered whenever I mention another guy. Why does he care who I date if he doesn’t want me liking him? He’s 21 and I’m 18. Also, as most of y’all jellies know, I haven’t been with anyone.. Er, shall I say “physically.” Lol. Anyway, he also seems to be on his best behavior when around me. I mean he barely cusses, acts mature and is all around a seemingly sweet guy. We also flirt on and off, but lately he’s been avoiding me since he told me about his sex addiction. Any suggestions?

Oh, when he was with my brother, my brother said he was talking about getting girls and that he only has girls for himself (the guy I like). So which side should I believe? My brother is somewhat a compulsive liar from time to time.