The gay cousin's Favorite

Plot bits and indicators are dropped during the sex scenes. Usually when a story has this much I skip them, like Full Volume. But in this story you have to read them because there are clues about the Mugo's identity and psychology as well as where their relationship actually stands.

The way these two characters are written, with the situation they're in, sex is actually the only way to make them communicate intimately without being incoherent with the characters' personalities.

While your criticism could have been valid for Full Volume, where the sex scenes are pretty irrelevant 90% of the time, this isn't the case here.

It's just added scenes that won't kill you, and in this story it is actually relevant, not for the sex itself but rather for how the sex is inserted in their relationship.