Responses
Maybe this?
http://www.mangago.zone/read-manga/akunin_o_nakaseru_houhou/
Not a oneshot though.....
This one maybe?
http://www.mangago.zone/read-manga/otonage_karikawa_seyu/
"secretary" from Minase Masara
http://www.mangago.zone/read-manga/secretary/
And he's having an affair with the Uke, who I think works in the same office as him. The seme seemed older and well dressed... that's all I remember about him. I think it was a oneshot. In the end, the uke realizes he actually loves the seme, but thinks that the seme wants to break it off with him, and stops seeing him. Although, really the seme was just working to get a divorce so he can be with the uke.
I've looked everywhere for this yaoi, but I can't seem to find it!