OP, you need to leave, to save yourself.
We recently lost a male relative, age 41, due to alcoholic heart failure.
His alcoholism had been triggered by a number of genuinely traumatic events we think, but had been ongoing for about 15 years. He was largely estranged from his DC, couldn't hold down a job, and was very unwell at the end. He was diagnosed with liver problems about 10 years ago, and heart problems more recently.
He had a very supportive and loving family overall (despite them socialising a lot with alcohol unfortunately) and they supported him through a couple of residential rehab attempts, and other treatment.
But his first love, in the end, was alcohol. Whilst there had been traumatic events in the past, there were also a number of occasions when he could clearly have 'turned things around', but he did not, very sadly.
Now he has died, we feel relief. Our grief for him was experienced while he was alive, and now we grieve for the lost opportunities that he could have had. But we also feel relief - that there will be no more calls that he's gone missing, or been picked up somewhere, or has had another health scare, or that he rings us in a state himself. Or indeed that he lets his DC down again.
It's tragic overall. It's monumentally difficult even when the will to change is there.
Save yourself, please - do your grieving for the lost opportunities (yours and his), and then look forward to the next chapter of your life. Your DP may be reasonably functional, but this is no life for you.