Hi.
It's yaoi, plot starts with seme still in school. he liked his brother's friend who was older and surprise kissed him. the friend ran away and then there's a time skip and the only part i remember is that the two ended up living next door or in the same building and the friend had a shocked and horrified face and ran back in his apartment when he saw the seme.
thanks for any help you can give

Sangen Tonari no Tooi Hito?

that's it, thanks 😀