Why does my freind keep trying to convert me?

I am an athiest and i dont want to be a christian but my freind keeps bugging me about it. he is a catholic and he tries to convert me at least twice a day. i have tried telling him that i dont believe in god but he gets mad at me. one day he got really mad and then punched me so it turned into a fight and i got suspended from school but since it was considered self defense on my part it didnt go on my record. i really want him to stop and i am really tired of it. can some of you give me some advice on what to do? dont tell me to covert and dont tell me im going to burn in hell im kind of depressed right now.