This is another post I could have written myself. Honestly, I think a lot of this probably is his untreated BP. I know what I have endured with my wife & seen how her father was as well & the paralells are right on. The anger, hostility & constant degrading seem to be classic sighns. I don't know what to tell you as far as stay or go, I know you are going thru hell right now staying though. Hopefully when you go to the docs you can get meds adjusted & that will help, but that hinges on him being willing to do his part. The only other thing I can tell you is to do like you did before & wait for a time when he is lucid & rational, then very nonconfrontationally explain to him how his behaviour is affecting you & your relationship.
With the custody thing, I really don't know, I have never looked into it & things are different in every state. But I can't imagine why you wouldn't get full custody under the circumstances. Plus given the fact that you are the mother gives you a great advantage on that front. Back over christmas when my wife was doing her whole I'm moving out thing, she started threatening that she was going to leave & I would only see my son on weekends & all that. I sat her down & explained to her very bluntly, if she walked out, she walked out alone & she would be the one getting weekend visits & because of her sometimes violent outbursts toward me, it would probably be supervised visits. She said she didn't believe I would do that to her, so I simply told her that no, she would be doing that to herself by the decisions she has made. I haven't heard anything else about it in a few weeks & she has been a totally different person, so maybe she has seen the light, although she is probably just in a smoothe spot right now & the bottom will drop out again soon.
I hope this has been at least a little helpful for you & I hope things smoothe out some so you can maybe get him to come around some.
"The struggles make you stronger, and the changes make you wise, and happiness has it's own way of taking it's sweet time.
Gary Allan- From "Life Ain't Always Beutiful"