I think it was really in the past. He believed that Seungho would always keep him by his side that's why when Nakyum came, he can't accept the fact that Seungho has eyes for someone else. He can see that Seungho is different when it comes to Nakyum. The flashbacks just show that he was just overconfident with his relationship with Seungho, that it will never change. Then, he has the guts to pretend as Seungho's father, what a bitch.

Read at your own risk..
It's just my theory.. On ch59 the first part wher jihwa has short hair, i was thinking its his older version and happens in the future? So maybe nakyum went missing and years passed. And seungho went crazy then jihwa was there to console him??? So probably they've been together for years...what are your thoughts in this??