He probably gave himself a big pat on the back for being so 'progressive' even though deep down he didn't like it.
Then he rationalised it and consoled himself that you were probably making a pittance anyway.
Over time, he's shaped this view of you as maybe some downtrodden 'trapped' woman stuck in a particular line of work through circumstance and necessity, scraping by and 'having' to do this.
Then he's got the shock of his life when he's heard the real income figure, and it doesn't correlate with the image he's created of you.
He's insecure, and misogynistic - because men dismiss things like Only Fans as 'easy money', and some even see it as grifting/conning men. And men can't do it too as the market isn't the same. So they hate it, it's one of the only things where men can't snatch a piece of the pie themselves.
I had a sort of similar experience. I wasn't doing anything like this, but my BF was so shocked when he heard how much my business made, and after a few drinks I stupidly joked, 'Oh yeah, it's all a front, I secretly do Adult Work.'
It was a stupid joke I thought nothing of, but my god, he became OBSESSED with finding proof. He was so insecure, and so jealous, but also thought so little of me that he didn't think my actual business could possibly earn more than him. It was a nightmare, we inevitably broke up, and years later he's still convinced that his narrative of his image of me is right; that I led some cunning double life, I'm a compulsive liar, and my real business was all a front.
Sorry to go off track but the point is once someone has an idea in their head about you, it's pretty much impossible to change it. His deep seated beliefs will rot what's left of your relationship from the inside. Can you really move in with him and live with that day after day?