Don't know whether to stay or go

My husband has stage 4 cancer, I still work. He gets around ok and is still going through treatment. Him and I don't get along for longer than a day. I'm making him miserable and he drives me crazy. If I leave he will die in a month. I am going crazy, I am angry all the time. I snap at him all the time. I'm starting to drink more than I should, I feel hopeless.  I feel like I should leave so he wont be miserable in his last whatever time he has left, but I don't want to feel guilty either. But I feel cruel and selfish if I go. I know I am not making sense.  I just don't know what to do. 

Lisa