i don't know if anyone has already wrote this but according to me, because Matthew was calling jin by his 'real' name Cheungwoo i.e, the name given by that oldie boss and also because of the boss used to call him by that and drug him while having s**, he's subconsciously thinking about him. I don't think he wants the boss to be fuc**** him, it's just happening without his control
need bl manhwa recs!😔