I would have liked to see them delve into that too, but at the same time I loved how they brushed past it. The sister didn't succeed in breaking them up, the fact that Tetsuya was married before didn't make Oumi question their relationship or Tetsuya's sexuality, he just accepted that it was part of his past.
Yes I agree that he just accepted that it was part of the past, but I also want to know how the seme would react regarding the reason why the uke break up with his wife before, because it was also the same reason why the uke and seme got into a quarrel or fight.
The manga has little smut, but it is much focus in the well written plot. However, it is sad that they didn't involve the talk about the past of the uke, it would be really nice to see it though especially if the seme recognize the pain of uke's past relationship.