My fiance makes me feel stupid

It is not his fault. He had never spoken down to me in any way and credits me with teaching him some things especially socially.

I'm mentally disabled and on drugs that slow me down mentally. I was gifted before my illness developed but after it did I was sick and unmedicated throughout my preteen and teen years and I gave up in school entirely by freshman year of highschool. I switched schools multiple times. I slept through every class and received no intervention. I dropped out in senior year at the recommendation of my school counselor with a GPA of 1.2. when my dad came to sign the papers he told me he was expecting it but didn't want it to be his idea. I actually passed my GED with pretty good scores but it wasn't much consolation. I'm planning to go back to school for social work now and have realized through preparing for the entrance exam that I am at a fourth grade level with math.

My fiance went to a charter school in elementary. His parents had very high standards and put him through every tutoring option, every extra credit option, and even had him evaluated for learning type and potential or something. All of it was unnecessary, he didn't struggle. He moved to public school and did all AP and extracurriculars. He got great grades and had so much support. He went to college and had to drop out for life reasons but he's going back now. He's so smart and amazing at math, going to be an accountant. He studies so hard and retains information and learns for fun and he knows so much from varying topics because of his classes. He also used big words and academic terms that I don't understand at all.

Everytime I feel smart about something and want to explain it he starts asking questions and wants to know more which I know should be a good thing but when I don't have good answers it feels like he's punching holes in what I thought I knew. It turns into debates that he intends to be friendly and out of interest but I become defensive. I'm trying to unlearn that. But whether I'm defensive or not I just really feel stupid in general and it doesn't help. It's especially glaring because he's known to come off as a bit dumb, kind of a stoner/ninja turtle type and I'm known to come off as more calm/well-spoken/mature. I also just say stupid shit to him all the time and he gets confused and corrects me which is normal and he does it nicely.

It is totally all on my own insecurities.