The Lover by Christopher X Sullivan

An asexual man falls in love with a male model… and is introduced to the fine art of getting down.
Chris and Mark are officially a couple… though Chris isn’t out to his parents. Mark, on the other hand, is trying to mend his broken relationships with his father and grandfather.

Their new romance is a source of stability for Mark and chaos for Chris. Together they navigate the many pitfalls of their newly sexual intimacy. Meanwhile, Chris can’t keep his family out of the loop forever because his mother is an especially gifted amateur sleuth.

Also, it doesn’t help that Mark wants to show off their romance like a first grader who brought a puppy to show-and-tell.