Sounds to me like he's kind of... obsessive.... lol

I would be careful, whatever course of action you take.

I can't bring myself to believe that not breaking away from him (actively, rather than passively- like you've been trying) will result in any change for the better.

Maybe you should just not pretend to be nice to him? Just show your real emotions. I'm not saying be mean to him, but maybe you could just show your disinterest and aversion in a slightly more direct way?

Don't engage him, and if he engages you don't commit to anything with him (party, etc), and keep your communication flat and short. Maybe he just doesn't realize that you don't like him? A reasonable, sane person would, at this point, realize this, but he does not sound reasonable or like a shining beacon of sanity.

Maybe, with him, it's like how children don't learn to stop doing something bad when their parents just ignore that bad behavior, rather than reprimanding them? I dunno. I've seen this in people, where they take on childish characteristics for some reason. Maybe they have brain damage, maybe they have a personality disorder or some mental illness? Who knows.

Anyway, hopefully he will eventually get the point.

Of course, there's also the option of just telling him "You just don't know when to stop, do you?" or outright telling him to fuck off. But it's hard to say how he'll react.

So, yeah, I'm really helpful.