I share some of your experience regarding BF saying he can stop then phoning up drunk and denying he'd been drinking, then saying it was just 2 drinks etc etc when it was obvious it was way more than that. My BF too is an amazing person when he isn't drinking, although he still has major depression issues.
I have also had the heart-to-heart chats telling him he needs to stop because he is wasting his life and killing himself (even done that with his mother and a psychiatrist) and it seems to sink in for a few days maybe, then it's back to square one.
I can only empathise with you I'm afraid. I can't give you any answers as I am also looking for them. Just know you are not alone, and I still have plenty of hope for my partner and relationship, and it sounds like you do too. Good luck.