I have some Info of him, but it might be a spoiler.
Ahem
Throw it at me pls
It seems like he already is in a relationship (or was just making out) with a man, because Makio saw him in a bar and he is an Uke (the author made it obvious, because she said in an extra page "Uke bath" and there were only Makio and Wachis friend)
When did this happen?
The talk between Makio and Wachi's friend happens at the end of Volume 4 in an extra. In germany the 4th volume was already officaly released, so I already read it . But here it the moment where Makio sees him in the bar: http://www.mangago.zone/read-manga/kuchizuke_wa_uso_no_aji/bt/sa-v4c002/pg-24/
Kinda hope wachi's friend gets his own happy ending tho
It's like he admires him a lot and i just :))