My boyfriend sometimes makes me have to poop during sex.

Okay so let me start this off by saying we do NOT have a fecal fetish or anything like that. However, I do have a lot of stomach issues. If I eat a single grain of rice I’ll immediately have to use the bathroom. So I’ve limited myself to one meal a day. My boyfriend knows about my stomach issues. Sometimes when we are doing the deed, especially when doggy style (which is unfortunately his favorite), I find myself either having to slightly pull away or clench because it feels like he’s fucking the shit out of me quite literally. Even if I don’t eat for the entire day it’ll still happen. I thankfully haven’t had an incident yet but I’m terrified I will. I like the rough sex so I don’t want it change, but even sometimes in missionary he’ll hit something in there and it HURTS. I’ve never had this problem with anyone else and he’s about average sized maybe slightly longer but that hasn’t affected me before. I don’t know how to tell him nor do I really want to but it definitely kills the mood sometimes when all I can think about it not shitting myself. This is absolutely embarrassing to admit but I had to say it to someone.