You were practically a child compared to him, Poet.
That story makes me so sad for you - you went to so much trouble for him, trying to do something grown-up and lovely, playing the role of a loving partner, and he treated you like shit. I'm disgusted that he belittled you, degraded you, and then had the temerity to call you immature - not that you were (he was!), but well, what did he think he was going to get, dating a literal teenager while in his thirties?? Maturity?
No, he thought he'd get someone easy to control and coerce into fawning for him, whose lack of experience he could use against them, and sadly that wasn't wrong. You didn't stand a chance against him, Poet.
He behaved like an abusive arse and then as the cherry on top, made you feel guilty for reacting with understandable upset, made you feel small and worthless, and invalidated your reasonable feelings, and made you doubt yourself. He positioned himself as right, and you as unreasonable and incapable, despite it being the other way around! And it seems that pattern has continued throughout your relationship, both covertly and more overtly.
I'm glad that you can see his meeting with your mum was probably a calculated, manipulative move. It's upsetting that he did something he knew you wouldn't want him to do, and chose to partially disclose that something 'awful' had happened to you.
That was a power move on his part too, imo - he knew that you wouldn't want your parents to know, and he showed you that he had that leverage over you and could disclose it and make you vulnerable and exposed at any point. It also had the effect of creating stress between you and your mum, and making you draw away from her. He was talking himself up to them, while simultaneously subtly isolating you from them.