Gagging/Vomiting after jerking off Fiancé

Je
Okay. So this feels so awkward for me because I've never heard of anyone doing this but... when I jerk off my fiancé, when he cums I'll gag and lately I've even thrown up.
I have no idea why I'm doing this! He doesn't smell or anything gross. And it's weird because I don't do it if he jerks himself off (just at the point when he cums). I still gag but it's light. If Im jerking him off when he cums though then it's a totally different story.
Has anyone else had this issue?
What'd you do?