help me remember the title

there's this bl manga I read but I forgot the title I want to re-read it. The story goes, uke and seme are some kind of researchers and uke likes seme but seme is getting married so uke created a clone of seme and decided to live with the clone after the wedding of the seme but it turns out the seme knew about the clone exchanged place with it before the wedding so now seme and uke lives together until they're old uke died first and left a letter to seme saying that he knew that he was the real one because he realized it after they live together and the seme was crying