tall uke in love with a short seme who is straight so he stole his girlfriend

i think it was a side couple in a manga where the uke is the older brother of one of the main characters? the uke has been in love with a guy that's shorter than him since school, and whenever the guy got a girlfriend they somehow end up falling for the uke. the seme eventually confronts him and the uke tells him to use him as a replacement or something (he's very insecure about being taller and that he's a man). they have sex in a car for the first time, and then in a bathroom the next. i have been thinking about this story for years and i just can't remember where it's from.