Okay, so I'm back to this post since I read it earlier and I was going through the same thing only a few months ago. I understand entirely that you probably love this person or are in love with them. It makes it harder to leave; it makes it harder to give up on a possibility that they would stop saying and doing the things that hurt you. It's hard to let go of someone like this if you deeply care about their well-being and just want to be there for them when things are hard and when things are really good, I'm still struggling really bad to let go. I don't know all the variables of your relationship with this person, so I'm just going to go off of what I know from this thread, so I'm sorry if I assume wrong or the things I say really don't help. His behavior is that of someone who doesn't care about how you're doing or if you're doing well. If that was the case, him making fun of you and saying "kys" a lot would stop and he would make it a priority to make sure you got better and that things between you two were improving and getting healthier. Everyone that has said he isn't a good person to keep around is right, he isn't. This relationship is toxic as you're aware you feel deeply enough that you can't live without him because you've been deprived of the love and attention that every person needs. Listen, don't listen to the criticism you're getting about you being in an abusive relationship like this one. Don't even pay attention to people arguing in your comments

I saw one person say that he was stressed out too and that may be the reason why he said that, but literally no one with any basic human decency would tell someone to do that just because they're are stressed or upset/frustrated ( not criticizing the person who said it, just helping the poster out :) ). If you feel like your situation is, it's not your fault you're in an abusive relationship and it's not your fault he is treating you terribly. At all. It's not. I started cutting when I was with him earlier this year, and it barely did anything for me, but I can see how it may be one of the last few things to help you feel better somehow. Nevertheless, it ultimately leads to nothing. Please, don't continue to cut and try finding other ways of getting things out. I heard using a rubber or hairband on your wrist helps to replace cutting and you could try that.
I'm trying my best not to overwhelm you with a giant paragraph but if you need to talk about what you're going through or you literally just need someone to talk to at all, or need any help in taking steps to leaving him, just let me know.