There's no implication that he's 'dating' Minhyuk. He just says Minhyuk's name and asks where he is/why he's here/why he can't remember anything before. It's also pretty unclear whether he truly forgot about Taeseung or not. Minhyuk says "The President is in danger" without saying specifically TS's name and SY appears to be confused by the word "President".
Whatttt????? He don't remember taesung?!!!!! (╯°Д °)╯╧╧ temporary amnesia right?
Yeah I wanna know if it's temporary too
So sooyoung got amnesia and he thought he was dating minhyuk not taesung? Minhyuk fans really has been waiting for this to happens i guess?