wait there’s a bunch of fart fanfics out there and I don’t know?
hm hm hm I dunno, friend. maybe be like ‘I like it in fiction, it’s a nice humiliation kink’ or something? (… and if you like it RL as well, just wait how he reacts to that to maybe explain a bit more lol)
but honestly, if you don’t want to explain, you don’t have to explain. simple as that. Just because he’s your partner doesn’t mean you have to be accountable for everything towards him.
In any case it should ABSOLUTELY be NO PROBLEM and should not change his view of you. If it does, something is seriously wrong with him.
It is just a kink. just because you enjoy it doesn’t mean you two have to indulge in it/talk about it/whatever. your relationship has worked before he knew that about you, and it should absolutely work afterwards as well.
bottom line: you should not be ashamed of what you like. you can be shy, maybe embarrassed, but definitely not ashamed.