I'm trying really hard to find this manga!
The seme is a rich guy, and the uke comes from a dismissive family. They met when they were kids. The uke is mistreated by his family, but I'm not sure why. He has a brother who looks exactly like him and is adored, while the uke is pretty much ignored (but his brother isn't a bad person).
When the seme tries to find the boy he met as a child, the uke's family thinks he’s talking about their favorite son. They don’t want to let go of their beloved son, so they decide to have the uke pretend to be him.
When the seme and uke finally meet, they slowly start to develop feelings for each other. The uke looks kind of childlike, similar to the main character in Okane ga Nai.
I've searched everywhere for this manga, looking through different tags, but I still can't find it. I'm getting desperateee