Is he rlly gonna leave him once he reciprocate his feelings

I think he won't (๑•ㅂ•)و✧ I believe that the blush and grin we saw on the last panel is the reaction he can't stop showing because he believes that Seyeong will be reciprocating his feelings (≧∀≦)

No worries.. Heejae rly head over heels for seeyoung he would never leave see young ! Spoiler :

They will move in together