As far as I understand it seems like Ian wants to end what he has with TJ and wants to move on from him. Maybe that's why he sleeps with other men. But at the same time he can't really move on from TJ no matter how much he tries. They have codependency problem. And he is in denial, he doesn't really know what he really wants.
1. It's more like a sheltering kind of relationship. Sex is more like a coping mechanism to ignore any problems or feelings. I think we can get a good understanding when we know how they get to this phrase.
2. Ian sleeps around in order for him to actually fall asleep because without sex Ian can't sleep.

I didn't finish the whole thing yet. But can someone explain to me few things?
1- What is the nature of Ian and TJ relationship? Are they ex lovers became friends with benefits? Or they have never dated before and always been friends with benefits? And if they're friends with benefits, why they have never dated bcs it's clear they have feelings for each other?
2- Why Ian fucks around with other men when he has TJ?