Why does he stay with me?

He obviously isn't fully invested in the relationship like you are. What you thought started out at so great and so strong might have just been a fling for him. You know by now that you can't make someone have feelings that you want them to have so my best advice for you would be to just start distancing yourself from this guy. It's going to suck and it's going to be hard at first but you're going to find that you're better off without him. If someone doesn't want to hang out with you as much as you want to hang out with him, then he isn't the perfect match you thought he was. You're idealizing him, you're making him out to be so much better than he is because you're in love with him and you're failing to admit that you can do better and you will do better when you just let him go an dmove on. Everyone deserves to be loved. So let yourself have that. This guy might not be a horrible person, he just isn't in love with you.