I'm not an expert, but wanted to say well done for taking the first steps, and please don't go back to him. And please, please don't have kids with him. You clearly care about children, given your job. The guilt you will feel for bringing a child into this situation will eat you up inside.
The phrase which comes to mind when reading your update about his wheedling and gaslighting is: you can't reason with unreasonable people. So don't try.
It is not up to you to justify your decision. You're an autonomous person who makes her own decisions, and you are perfectly entitled to leave him for any reason at all- regardless of the abuse you have undoubtedly suffered.
Would it help to come up with a couple of sentences, that you can either repeat to yourself as a sort of mantra, and/or say to him? Words that simplify the situation, that don't engage with whether what he did was a big deal (it was) or get you tangled up knots/ argued out of your decision.
eg "I am ending the relationship. I don't want to be with you any more."
There isn't any arguing with that, is there?
Stay strong OP. Do it for yourself and your future babies.