Boyfriend smokes weed when we fight?

my boyfriend and i are both 22, we have dated for 10 months now. i know he cares about me a lot, but the times we have got into fights he has gone to his friends and smoked. i admit to him after the 2nd month of us dating that i absouletly hate hate hate weed! i told him i would not date him if he continued to smoke. so he stopped but has slipped up quite a few times when we fight. he always puts the blame on me by saying "if u didnt act the way u did i wouldnt have smoked" or "the thought of loosing you caused me to smoke to help me relax" i just think they are excuses because we have split up and got back together a lot. he knows we wont break up for good. what scares me is in time after being together and living together, i have to fear everytime we bicker he will run off and smoke or smoke in our apartment. its healthy for a couple to argue, but he cant handle any kind of arguement. and i think its completely bull he blames me for his slip ups cuz a stupid fight we get into. what do i do and what do u guys think about this?