It will be much worse if you stay and he drinks himself to death in any case. You cannot live his life for him and he has to make his own decisions. And he will not quit drinking FOR you, he needs to do it for HIMSELF which doesn't mean he loves you any less.
Alcoholics are living in denial most of the time (and a strange kind of lapsed time frame as well) so the previous separations are not going to be taken seriously unless you actually mean it. It is no good if you keep coming back all the time - it means to him that it is ok with you if he carries on drinking.