Is my relationship doomed?

my BF and i have been together for 2 years, we were friends B4 that for 3 years. i am 23 and he is 22. he works constrution about 50hrs a week, and i am in an office jpb working w/people who have mental dissabilities. lately he seems to get mad at me so easily and it really hurts me. i try so hard to be strong but i am falling apart. i tried to talk to him about it but he just says im always pissy. this breaks my heart. i am really trying to be a better GF. we have talked about marriage and gettign engaged. he says he wants to and will buy ring once have money. i am scared. he calls me stupid and dumb whenever we get itno fights, i told him i really dont like that at all. and he shouldnt call me names. he will say he is sorry. i am so upset right now. i started to talk to him about how i felt last night, but he said he didnt want to fight, and he started humming so i couldnt talk. its jsut he is so hard on me. and i know his job is physically hard, but i work too. :(