Emotionally/verbally abusive partner advice...

So without making this an insanely lengthy post I’m going to do my best to keep this short. I’ve been with my fiancé for 7 years and we have a 7 month old son together. He has an 11 year old from first marriage. (50/50 custody) He has been verbally and emotionally abusive for quite sometime now to me and from time to time to his 11 year old. At times before it seemed to not be a constant thing and something I felt I could deal with given some of his other qualities that I looked very highly on. When I became pregnant I feel like things became steadily worse and the occurrence more often. A couple months ago I left with our son for a week and went to my moms because he accused me of something I did not do and wouldn’t accept anything but me to fess up (which I wouldn’t because I was innocent) he blew up and while I was hold our son said some extremely horrific things to me and threatened me. My plan was to seek full custody and move on with my life because many months prior we had an argument where he said for me to leave and take our son and he’d just cut me a check every month, he didn’t want any custody. Well...turns out he said he would ask for shared custody. After I did more research I learned that based on verbal abuse the courts will usually default to 50/50 custody. I decided to go back with the intent that we would work on “us”. He said he knows he has a temper and wants to make things better. 2 months later and well things are not better and in some ways worse. I have started to record his blow ups and abusive comments whenever possible (which is proving difficult but I have a few recordings) I want some hard proof of his behavior if down the line I have to leave. So my question...has anyone had any experience with or known someone who was successful at getting full custody of their child based only on emotional/verbal abuse? I love my son so much it hurts and I could in no way shape or form not see him half the time especially knowing I’d be leaving him with such a hot headed person. TIA!