You have enough sensibility to know he is shit partner, yet feel inclined to "apologise" to him for not being fine with that? You care far too much, perhaps in general. It doesn't matter he had toxic background if he has no intention of correting his ways. He doesn't even see his mistakes. You don't owe him anything. His problems are his own.

You also lack assertiveness. Have you ever told him upfront that he is acting in a toxic way and your behaviour is normal in relationship not his? Now, being his therapist in general is not what I would advice to you , or anyone else. With that said, not everyone can be changed with kind words alone. Sometimes you need to be both brutally blunt and consistent in your behaviour to make someone change. Again, it's not for you to do, it would be harrowing and traumatising experience.