You're Sunghoon best friend. You are his priority over his girlfriend

Sunghoon is Hannah's boyfriend for many years, he is sweet on her but he almost priority you, because his relationship with Hannah just for formality aka just as 'status', he's not love her at all. So, he loves you more than he loves her

Today is your birthday

"I'm just going to Reena love, it's her birthday today, I love you!"

He said and left her alone even it's her birthday too and go to your house