Forever After by Marie Sinclair

After a fire destroys his apartment, Diego has no choice but to move in with the person least likely to welcome him with open arms: Alex, the recently divorced, presumably straight guy who didn’t take kindly to Diego hitting on him at a friend’s wedding.
Unfortunately, Alex can’t exactly complain about the living arrangements. After his wife cheated, he moved across the country to San Francisco to start over. The place he’s living belongs to a friend, so when Jake also offers Diego a room, Alex needs to figure out how to deal with the exceptionally hot, sex-positive, queer youth counselor whose gaydar has picked up that Alex isn’t as straight as everyone thinks he is.
Forced to live in the same house, Alex and Diego are about as combustible as fire and gasoline. But when Alex’s thirteen-year-old comes out as trans masc and moves into the house with them, Alex begins to see another side of Diego, and Diego realizes this sullen, complicated man has a heart of gold that’s been stomped on a few too many times.
Once the walls start to come down, Alex and Diego realize they have a lot in common. Not to mention an attraction that blazes hotter the more they get to know each other.