There are some men who do change once they are sure of a relationship. While courting, they are perfect gentlemen. But once they feel secure, they drop the facade. It’s as if they enjoy the “hunt”, not the stability of a relationship.
For your own sake, please take a big, big step back from this guy. You are unlikely to be successful no matter what communication “skills” you develop. He is controlling what you talk about, how you talk, and how long you talk. If you don’t agree with him, you are in for hours of being scolded.
Enough! He is gaslighting you when he says he hasn’t changed. He has. And it isn’t pretty. You deserve to be treated with respect and dignity, not like a not very bright child.