Oh, op.
You are not the problem here. Your dh is the problem, I'm sorry.
But in no healthy relationship do you strive to "live up to their standards".
He is verbally abusive to you when he drinks. It sounds like that he gaslights you frequently. He continues to belittle you and make you feel bad, to turn each situation around so that he is the victim, when you've done remarkable things in the last year to stop drinking etc.
You will never be 'good enough' for him. Not because you aren't good enough- you sound like the better person by miles- but because it's about control and superiority, and that is something you cannot influence.
It isn't normal to be "drinking" regularly. To have a couple of drinks or so, yes, but to drink to the point it affects moods, tolerance, behaviour? No.
What's more, and what signals just how dangerous he is, is that he sent you death threats. The police were involved. Your mother stood witness.
Men who send death threats are often men who kill.
Has he ever been violent to you? Pushed, shoved, hit, strangled you?
Has your mum said in the past she doesn't think he's good for you? Is that why she's kept her distance? It's very very hard for people to witness loved ones exist in abusive relationships when they can't see it.
Abusers are manipulative. They make it seem like your fault, like their behaviour is justified, that they are the victims.
Please read this page:
www.nationaldahelpline.org.uk/
www.victimsupport.org.uk/crime-info/types-crime/domestic-abuse/recognising-signs-domestic-abuse/
www.womensaid.org.uk/the-survivors-handbook/am-i-in-an-abusive-relationship/
You are worth SO much more than this. 