to be honest, I started seeing this series because of its OST but the show is so good, if you are seeing some BL dramas, I'll recommend you to watch this first.

summary;

This series follows three couples and focuses on two primary characters.

Orphaned at a very young age, Gui, a fourth-year engineering student, has always had to work hard to support himself. Despite the many difficulties, he has kept his soft demeanour and gentle smile, and his empathy for others. Whenever someone struggles, he is always one of the first volunteers to help.Solo, a freshman music student, has everything: money, fame, good looks. But he lacks a smile. After his mother's untimely death, he lost his happiness. Nothing could fill this missing hole in him until late one rainy night he stumbles into a café for coffee. At that moment, their two worlds collide. For a cup of hot milk and a warm smile, Solo returns to the cafe every night. And Gui waits for his late-night visitor. Night after night, the young men continue meeting at the same spot and as they see each other more frequently and their lives overlap, the two become one another's breath... a necessity, just like oxygen. 

link (youtube); https://youtube.com/playlist?list=PLYYyUhZKiEj5ch0D24-wlDbTifB7lTS7Y