Wow, I could have written this myself. I was married to mine for 22 years and he acted exactly like this, even down to the mental health issues for which he was medicated but refused to take the medication.
Him threatening to leave me during arguments was a regular occurrence and I would spend ages trying to talk him down. Eventually I just ran out of energy and the next time he said he was leaving I told him to go, it was what I wanted and don’t come back. He realised I actually meant it, as he headed for the door I told him to take his stuff with him.
As he drove away, I felt myself relax. I realised this was in fact exactly what I wanted. He was gone for 2 hours and then I heard his key in the door, he actually apologised for being a dick, but it was too late. I had had a taste of freedom, it only lasted 2 hrs but it sure felt good, I knew then that we were done.
I totally withdrew from him, there were no more arguments because I no longer cared, I just walked out of the room and left him to it. Within the year we split up and my life changed for the better.
2 yrs later I met DP, he is the total opposite of my ex. No arguments, no threats of leaving me, no bad moods that last for weeks. He is a good, caring human being, who I look forward to seeing when he gets home from work.
I look back now and I can’t believe I allowed myself to live in that toxic atmosphere for 22 years. My advice, get out sooner rather than later, don’t waste your life trying to fix him, only he can fix himself.
Good luck OP, there is a better life out there for you, you just have to reach for it.