In Time with You (2011)

Both are about best friends who have known each other for years who can be themselves around each other. They know each other well, but they're bad at recognizing their own feelings and deny them out of fear of losing the other person.

similar plot - 2 best friends thinks they are only friends/siblings however they realise their feelings for one another.

if you love the movie, you should watch the extended version of Ariel and Chen Bolin love story in the drama... or vice versa

It's also the story of two best friends falling in love ..maybe the difference is that the man lead loved the girl from the very start but didn't show it in order to preserve their friendship..

It's kinda remind me for the synopsis "from long-friends who watched each other relationships and ended up together."

Housewife Miyazawa Tomomi, her husband out of a job, loses her treasured home as her family is forced to do with less during the recession. Her one ray of sunshine is her upcoming middle school class reunion, where she hopes to meet old friends as well as old flames. The class reunion, however, turns out to be more of turning point not only for her but for the others as well. At the party, she reunite with her old friends Sugiyama Kosuke, Nishikawa Yoko, Okubo Shinichi. Just how will these four people's lives change after their class reunion...

they share a theme of best-friends developing love... eventually

The guy loves the girl but the girl takes her own sweet time and dates another guy. Both dramas need patience to see OTP together but the wait is worth it!