Really, there’s no point in trying to understand why narcissists are the way they are. It’s a legitimate personality disorder that is unlikely to change… and lots of times, I’m noticing that they have at least one parent that is very enabling. Sounds like his mom is his enabler. That’s also unlikely to change because neither one sees anything wrong with his behavior.

You just need to stop letting yourself get sucked in. You know better at this point, right?  No matter what you feel for him, you know your life is better off without him in it, so that is a boundary you must set for yourself and stick to it. Push HIM out before he pushes you out.