I don't quite remember the exact details of this situation, but he may be doing it because he's insecure and he knows that he can always come to you for a source of validation.
The situation was: we know each other from a long time ago but never were friends or anything like that. I told him I like him and he said he liked me to but isn't looking for a relationship / doesn't believe in relationships, etc. That was about 4 months ago.
He probably have have some serious issues, sometimes it seems like he's an asshole to anyone else but me (or something along those lines). He was very upset when I started dating this guy he knew, warned me about him, etc. He seems very protective about me, which is weird, he told me yesterday (jokingly) that anyone who wanted to date me had to go through him (yeah, he's probably just fucked up in the head).
He knows the kind of guy I am (too nice, naive at times) so he sort of wants to protect me from himself and from other guys.
At the end of the day I obviously enjoy his company/attention, having someone to talk to pretty much everyday about anything. Is it worth it, though?. We fell out a bit while I was dating his "friend" so I know that it's doable, but right now I'm just lonely so it's a risky situation.