Responses
I think this is the one http://www.mangago.zone/read-manga/houtou_musuko_to_koi_no_ana/
I only know something similar to this but they’re cousins. It has the same age gap and scenario, dude goes to countryside, chasing an afterimage of his older cousin who he thought was a girl but is actually a guy. Guy is also his teacher. Teacher is gay and was caught masturbating.
http://www.mangago.zone/read-manga/houtou_musuko_to_koi_no_ana/
There is a yaoi where a high school boy goes to the countryside to live with his grandparents and hes hoping to see his beautiful aunt but his aunt is actually a boy and things happen and he sees his uncle masterbating jn the middle of the night and gets caught watching him. Btw the uncle is a teacher. It was translated by galaxy does bl but i cant find it anymore.