Official Soundtrack links:

1. OST Part 1 

https://www.youtube.com/watch?v=fSpVm9BR9S0

2. OST Part 2

https://www.youtube.com/watch?v=AzXUTAMjhVg

3. OST Part 3 (written & sung by Yoon Seo Bin, the main lead who plays Choi Min Hyun in the drama)

https://www.youtube.com/watch?v=iJiBzD3-xpE

4. OST Part 4 (english version of OST Part 3)

https://www.youtube.com/watch?v=X6DmgJsmk9s

My favourite song is the 2nd track, especially when it goes "Don't you fade away without me knowing." Very fitting for this drama. What's yours?