I'm so sorry you're going through this!
I've been in your partners position myself. My ex was a raging alcoholic, was suffering really badly from depression and was mentally and emotionally abusive.
The longer I stayed with him, the more I started to resent him as he wouldn't help himself. Every time I wanted to leave he would threaten suicide. My mental health was also suffering as a result.
It was truly awful on both sides.
I know you don't want to here this OP, but you really need to be on your own, get yourself better and find true happiness again, then someone else will come along and you'll be thanking your lucky stars that things ended to up the way they did.
If you haven't already spoken to your GP, then please do so.
If you have private health care through work (such as AXA) you can get 12 sessions of therapy free.
If not, there are many free organisations out there that can assist when it comes to speaking to someone re your mental health.
Please go walks, get fresh air, listen to music, read, eat healthy, speak to family and friends, write down your feelings/journal and meditation!
Please please look after yourself.
I know it's really shit, but dont beg him to stay. If he needs to go then you have to let them!
❤️