in front of him

This may be a weird topic but I'm being legitimate. 
I've been with my boyfriend for a year and a half, we always have sleepovers and stuff and sometimes he stays over several nights in a row (like 4+) and I will not poo even if I need to. I'll either wait until he's in the shower or just hold it until he goes home. Why am I so shy? I don't fart in front of him either. Yet he poos all the time when I'm around or farts on me and everything. Ahah how do I not be so shy? I'm going interstate with him for a week or two at the end of the year so I can't be like this. And especially since we plan to live together some day