It’s been a long time but it’s something like this. Uke and his brother lost their parents, they got adopted by this rich man who lives with his son (seme).

Uke goes to the same high school as seme, he has a crush on seme.

Uke goes home one day and accidentally sees his brother having sex with the rich dad. He told seme, who told him that they were bought to pleasure seme and seme’s dad.

Uke has to have sex with seme now, I don’t remember the details much but uke was really sad because his love, seme, only treats him like an object (or something like that)

If you know the name of the manga, please tell me. I really want to read it again. 😉

Try Saihate no Kimi e by Minami Haruka.