Responses
This probably has nothing to do with the one you're looking for but it reminded me of this so I thought I'd recommend it. "Ginmokusei: The Tailor Shop". Also if you search 'tailor shop' or 'suit shop' there are a few options. Maybe it's one of them.
Tysm for the recommendation! I'll read it. I also actually ended up finding the manga I was looking for! It was Iyarashii Mannequin
It basically has two employees from different suit shops (I think) and one of them saw the other one getting fucked in the shop
that's the most I can remember tbh