The uke and seme work in the same company, but the seme is straight. The uke always watches the seme in the lift at work, and they somehow have a one night stand. The uke thinking it was only a one night stand goes to a gay bar and the seme chases after him and tells the uke he's in love with him.
I think it was part of a series of oneshots but i'm not really sure.

Please and Thanks 🙂

I'm pretty sure it's a side story in either Kawaii Akuma or its sequel Itoshii Akuma  

Right mangaka, wrong manga. It's a side story from Scarlet.