From your post I can tell he’s important to you. I’m just a stranger on Reddit so take this as you should any advice on the internet. I would try to find out why this would trigger him so bad. It’s good to be sensitive to someone’s triggers, but he also has to try to work on his own. You had no malicious intent with your comment. He needs to recognize that. The problem is his to fix. You can help him. That is one of the things that help build a good relationship. Ultimately though, he has to be the one to get over it and try to work on himself. If he can’t, then you run the possibility of spending the rest of your time together walking on eggshells trying to not upset. That will have a negative impact on your self esteem. Don’t do that to yourself.