typically men who accuse their wife of being unfaithful are being unfaithful themselves.
he needs to get counseling for his alcoholism.
no doubt he is losing your trust with his story-changing.
i hope everything works out for you and your situation.
from what i have read, it would seem clear to me that he is seeing, or has seen, another woman. i dont want to sound harsh, im just blunt.
you though, are a very strong woman. anything that he has done is not your fault. i would suggest marriage counseling, because, obviously, you love this man. from what it sounds like, you already have your suspicions.
again, good luck, i hope for all the best.