Ah Leelee, there is no rational answer from someone not capable of being rational.
In my opinion addiction is (mostly) a mental illness. I say "mostly" because there are lots of addicts, some right here in this forum who achieve long-term healing and sobriety. So it's possible.
He made, and makes terrible decisions because he's an addict. That's what they do. Alcohol has such a grip on him that living in a car is more acceptable than giving up booze. For now. It could change.
As to why he treated you badly when drunk: I'm sure you know that is very common with drunks. Abusing alcohol makes most people aggressive and nasty. It's the nature of the drug. Of course it doesn't excuse the horrible behavior.
Try to let go of needing a rational answer. God bless.