I'm a big one for pushing people away. My advice would be to talk to him. Write a letter and tell him that you like him and you want to be there to support him but you are unsure of what to do. Ask him to give you guidelines of how he would like you to react to his "pushing away" behaviour.
It's a hard line to find.
Through counselling I was able to identify my behaviour that "pushed people away". There are many reason I did it. Mostly because I want to be loved but I'm scared of being hurt. People get close and I do things to mess it up. I still haven't worked out if I'm just a selfish bitch though. I don't think I am but I do things, I say things that aren't socially acceptable. I can be judgemental and apparently I have too high expectations of people.
I found with my mum, the only person that wont let me push them away, she would say things when I was in my hole that would seep in and hold for when I crawled out. She would test the waters so to speak and see if I was still in my hole or if I was out. She would take a break when she needed to but she would always come back. She would always say that she loved me. That she was here for me. No matter what I did she kept coming back until I finally accepted that she "did love me", that she would stick around no matter what.
It's horribly self destructive BUT. He must also work on changing. He is aware of his behaviour which is a good sign but he must also change and work with you because people like this, me included, can be very destructive to others so make sure you also protect yourself and don't allow his "pushing away" behaviours to harm your well being.