"totally captivated" is the only one i know of.....its later in the story....doesn't show them having sex but you can get the picture...
i vaguely remember i read something like this before, but i don`t know the same, sorry.
it was about a loving couple but once very week the seme disappeared and didn`t tell the uke where he went. one day the uke followed him and found out that the seme was blackmailed to have sex with a hetero couple...
this one or not?
http://www.mangago.me/read-manga/nigai_kajitsu/
ch2-3..
Hello world! As a pervert, I want you to recommend me some yaoi which: there is a seme and uke couple, but the seme is "being done" by someone else but the uke doesn't know, not threesome, foursome, or somesome else with the uke. Doumo!