My friends boyfriend is really clingy and serious with her?

So my friend recently got a boyfriend. I had a very short relationship with a guy I'd known for years, but we're still friends, and I think he still likes me, he just flirts with every girl. But that's besides the point. My friend has been seeing this guy for maybe two months now. She's 13 and he's almost 15. Her mom doesn't know about him. She's always spending time with him, and he buys her a lot of stuff like gift cards and jewelry and random crap she doesn't need. I'm assuming he comes from a well to do family. She always complains about how ugly she is, and she worries about her weight etc etc. she won't let me meet him at all and barely fills me in on anything. I know that he gives her a hickey a lot, because she wears turtle necks/a band aid on her neck, or covers it with her hair. She acts really weird, and keeps a lot of secrets and stuff from me. And he's holding her back because apparently he refuses to go to fairs, or swap meets or anything fun with her, but he goes to the movies all the time and gets lunch and dinner with her. She somehow managed to sneak off and go surfing with him one time too. Regardless of the fact that I think he could easily take advantage of her, I just don't like the whole ordeal. And no, I am not jealous whatsoever. I'd rather be with the guy I know than this dude. I just don't get it. Thanks for listening.