You need to leave, your number 1 priority is you, if you're not well, you can do nothing for anyone else either.
So get out, get yourself safe.
Is he being abusive intentionally, is he suffering serious mental health problems - only he knows.
It could be he just doesn't do sexual attraction or emotional connection - some people don't. If he doesn't know thats even a thing, he could be masking it and could have been doing so for a very long time without any way of putting it into words... and that could explain the flip flopping back and forth - he doesn't feel the love and attraction he thinks he should... but equally doesn't want to lose you and what you have together...
Or.. hes a total arsehole who likes controlling you via your emotions.
Or he is cheating, or about to cheat or.. who knows what.
The point is - his MH, his behaviour, his feelings - they're HIS problem. Not yours.
The fact he has done nothing to address any of this seriously, seek help anywhere, in any way means he's not really ready to make changes.
Whichever it is though, you need to look after yourself first, and to do that, you MUST leave!
IF he kills himself.. then he was going to do that eventually anyway. I won't tell you that people who say they will kill themselves never do because that is not true, some of them do. But if they do, when they do.. thats their decision, it has nothing to do with you.
When you leave and he contacts you and does the inevitable 'im going to kill myself' then your response MUST be to call the police and ask them to do a welfare check as he's threatened suicide. Thats it, nothing more, don't reply to him, just contact them and let them know where you think he is.