Please help me find this one yaoi. I think it was a oneshot. The seme is about to get marr...

Please help me find this one yaoi. I think it was a oneshot. The seme is about to get married the next day (or later that day) to the uke's sister. The seme and uke end up in the same room. The uke breaks down and they have sex. The seme tells the uke he's at fault for their twisted situation and this will be their last time. Seme marries the sister.