My (23F) husband (29M) thinks I'm cheating because I got a hemorrhoid

This is really embarrassing to post about, so please be sensitive.

My (23F) husband (29M) last night accused me of cheating after he learned I have a hemorrhoid. I'm completely devastated, and I can't seem to convince him to his (or my) satisfaction that I didn't and would never cheat on him.

He noticed when we were about to have sex that my butthole looked a little different, as it does when you have a hemorrhoid, and immediately asked if I'd cheated on him. I'd already told him earlier that day that I was having some pain, and even about a week before, too. It didn't matter, and he said I could've been just telling him "as a cover" so that he wouldn't be suspicious if he saw.

I tried explaining to him that hemorrhoids happen sometimes and that they're natural and it's certainly not because I had anal with someone else. His response was that they're "not normal for me." That's true, I don't get them often as an adult (only one other time in the three years we've been married, and he thought I was cheating then, too), but I still didn't cheat, I can't explain why or how I happened to get one now, and I'm hurt and angry. He treated me like a cheater, withdrew all affection, and won't talk to me like a normal person again. What can I do? Can I convince him? Is this crazy at all, or would most people respond like him?

TL;DR my husband accused me of cheating on him when we were about to have sex because he saw that I have a hemorrhoid. I didn't. I can't seem to convince him otherwise. Is there anything I can do, and is that a normal response in this situation?

ETA: we did anal once before and I got a hemorrhoid (or agitated a preexisting one, as someone pointed out). All he knows it what it looked like afterwards, and he claims I looked similar last night to how I did after we had anal. He doesn't think that it's impossible to get them any other way, he just saw a similarity and panicked.