please someone help me. im losing my mind. blond haired bottom and brown haired top. they ...

please someone help me. im losing my mind. blond haired bottom and brown haired top. they are basically playing a game I think to see who will confess first (?) but I think the blonde is just leading him on. its a manhwa. sunbae and the other guys name is haemin ??? i just remember a specific scene at the beach where the blonde says “whatever, i’ll just reject him so he remembers who has the upper hand” and the brunette says “sunbae…can’t you just be mine?” and the blonde crumbles and is red in the face and speechless.