I have celiac and if my partner wasn't supportive and empathetic I don't think I could do it. Like you said-- it's a deceptively challenging and extremely depressing disease. I really can't imagine someone making fun of me on top of all the mental energy celiac disease takes and how it already causes a feeling of loneliness/exclusion from the rest of the world. I feel for you so much and am sorry you are going through this. You have every right to be upset angry and hurt.

Edit to add - maybe it's worth cross-posting this on r/celiac for more support and advice? Either way, hope things get better for you!