If this Sungyeon was longing for Hosik even before they meet (I'm not sure if he remember his past life), there is a possibility our Sungyeon was longing too and that's why he was always so obsessed about him ٩(๑❛ᴗ❛๑)۶
He actually does remember. That's why he was so persistent on chasing hosik and went to such extremes.
If this Sungyeon was longing for Hosik even before they meet (I'm not sure if he remember his past life), there is a possibility our Sungyeon was longing too and that's why he was always so obsessed about him ٩(๑❛ᴗ❛๑)۶