ery good at getting people to agree with him that I might just be making things worse in my head
He is at fault, but you need to take responsibility for you. You need to take care of your emotional self. The part of your process that needs to change is the one above. You currently have a story that goes 'He treats me in a way that makes me feel bad. Whose fault is that? It's probably him, he's the one who's doing the unpleasant things. But then, he says it's me... perhaps he's right? I can certainly see that I'm not perfect, so maybe my actions are making him be horrible to me...' etc etc. All of this is self invalidation. You know what you feel. This story should be 'He treats me in a way that makes me feel bad. I told him, and nothing changed, so I'm leaving.'
There are no rules (other than laws) about how we 'should' treat each other. Everybody is pretty much allowed to do whatever they want; lie, cheat, manipulate etc, within the emotional realm. So the rules we all have to follow are the ones we make ourselves, as individuals, according to our own individual boundaries. Whether somebody is abusive or not is by the by; even if he was an absolute angel, but the things he did made you feel bad, you still would need to leave.
Feelings are all we have. If you're on a beautiful beach with a beautiful house and a beautiful pool and all the best food and drink and a million quid in the bank and lovely people around you, it means nothing if it makes you feel bad. And it could.
All the boundaries lessons in the world can be boiled down to 'Do things/spend time with people that make you feel good. Avoid things that make you feel bad.' What those things are, and who those people are, is up to you. You are in charge. You are responsible for looking after your own emotions.
So if he's regularly making you feel bad, and if he's calling you abusive, I'm pretty sure that crosses your boundaries. Nobody has to believe you or tell you you're right. Because you already know your own emotional responses to him, and nobody could possibly know better. You are the boss.
Validate yourself. Accept that your feelings are your truth, and nobody else knows a thing about how you feel, because they can't feel it.
There is lots of support out there, and it's great to access it and to use it to help you, and you definitely should. There's nothing rare about your situation; covert abuse is a well recognised concept, and there are ways out of your situation that many, many people have already successfully used. The best support you can possible have, though, is your own. Support yourself. Support your own feelings. Have your own back. If you feel bad, nobody can tell you that you're 'wrong' or that you have to keep putting up with it. Don't question yourself. Just respond respectfully to your own emotions; listen to what they tell you. It's like looking after a child. Your emotions say 'I don't like this!', so instead of responding with 'You're just being silly, be quiet!', say 'Oh, darling, really? OK then, shall we go somewhere else? Where would you like to go?'
That's self validation, and you sound like you really really need it right now.