Hi betshinhye,
I thought I should sign back in after seeing your post now that it's so quiet here at work here and all the ICU patients are asleep.
Yes, I do think he wrote if for Shin Hye as well. I've read threads and threads (GUILTY at work) about how JKS might have written this for certain costars and what not. There are threads that analyze and go into great detail about this song and how JKS wrote this around Sep or Oct, his depressed state around mid 2012, and how the release date of this song coincides with someone's birthday, etc, etc, yada, yada, yada...
But STILL, those details and facts don't sway me in my belief for GeunShin. My reason being that JKS is so honest and a free spirit that when he says "I Love You", he MEANS it.
On certain threads, they even talk about how he has expressed this before publicly to other gals so the song has to be written for someone else. The difference is that unlike the other gals he has said this to, he continues to keep in touch with Hacci even mentioning her mom now and then. (even visiting the family business for heaven's sakes!)
They continue to be in sync in so many ways and their friends and acquaintances (business and what not) continue to be intertwined.
I like how Hacci is still close to Hongki (and we all know Suk is buddies with that guy

and I even think Hongki and Big Brother hold a LOT of secrets about the two)
I just think that bonds break when two are no longer connected. In regard to GeunShin, the bond is seriously INTACT and STAYING STRONG!
That's my opinion anyways and what I've seen and learned in my own personal relationships. The song definitely resonates with me.
We all know Suk loves Hacci. He's already said it. He is after all his own company so he can freely express himself. But he has to protect others too so he has to restrain himself. That's what makes him a true professional and a person who leads and takes care of others.
Anyways, simply put, I think they're FOR REAL. And I need to get back to work and make sure patients are still breathing...