How do I get him to stop pushing me away.

That does sound complicated. Maybe you should just sing that Avril Lavigne song to him, and he'll get the message...jk. Anyway, do you know if he is out to his family and friends? If not, it's possible that he's scared of coming fully out of the closet. Also, this could possibly be his first intimate relationship, and he's not quite ready to commit. But it does sound like he's hiding something from you. For all you know, he may be cheating with you, and only starts acting like a bf when he's tired of the other guy. He may be bipolar or have another psychological disorder. Just try to approach the topic gently, but also annoyed. He needs to know that whatever you have means a lot to you.

 

Hey Cesar! X

It does seem like he is hiding something , but maybe not something bad. Just something he is uncomfortable saying. What I would do, is push for a deep and personal talk with him , tell him that you really like him, but for this to work, he needs to be open and honest .. As you can clearly see something is up with him.
As long as you focus on the positives and tell him how much you like him and wanna be with him . He shouldn't get defensive , but should feel more inclined to open up to you . Refer to the last experience you guys had, explaining you don't want a repeat of that situation , as you have both grown and come a long we since then, you believe this time round you can be better together if he just opens up to you, also Maybe play victim a tiny bit and ask 'have I done something wrong' that way he should feel some slight guilt and a little more obligated to tell you the real issue. Although unfortunately we can't rule out that something may be bothering him that you have said or done.... It's still the best way forward. Sit him down, or call him up . Face to face is best though I think.