There is not an official complete list yet released by the producers, but there are several playlists made by users on youtube with official OST's of the drama .Just search it's okay to not be okay ost playlist on yt  .

OFF:  My favourite songs and IMO the best  are : In your time (#1) , breath(#2) , Gonna Tell a Lie ,You're Cold and In Silence (but not official release yet) .

currently there is still no complete ost bc the series is not yet finished but you can find/download it on this link https://kdramaost.com/en/doramas/1801-it-s-okay-to-not-be-okay

I've listened to the OSTs on spotify. They have alot of the songs on there.

 MyMy:

Not all the songs are released yet, but the below list are the songs that are out so far:

- You're Cold by Heize
- Breath by Sam Kim
- My Tale by Park Won
- Wake Up by Elaine
- Got You by Ga Eun
- Your Day by Kim Ki Won feat. Kim Bom
- In Your Time by Lee Suhyun of AKMU

thank you :)

 Aline:

Which name of the song in episode 14? In that part after KT is on the other side of the door ... "i have something to say to you (...)"

I think it is “in Your time” by Lee SUHYUN 

 namu:

In case anyone is still looking for the songs, I made an unofficial playlist  when the drama started, in order of release https://open.spotify.com/playlist/1NYBNsuxqGxOnlGhY6cxSq 

Thank you :)