Maybe instead of calling yourself stupid and thus perpetuating his lies, you can learn to reframe. You can say, I'm not sure I am doing this right and I am scared to do it wrong. There's nothing wrong with that statement and it doesn't make it about whether you are stupid or not--which you aren't.

I get that it is hard. I have had to unlearn a lot of stuff from my childhood and past. It isn't easy. But it isn't impossible. And I believe you are capable of learning and changing for the better. You are hurting yourself by allowing this person's lies to be perpetuated by you. You are worth more than that. Give yourself a chance. Love on yourself a little.

Hang in there. Eventually it does get easier with practice. Sending you hugs. Kit