It Had To Be You 2005 on netflix

Restaurant supervisor Jill (Karena Lam) has a handsome boyfriend Chi On (Wu Bing), but she is just his backup girlfriend. She knows she is the other girl, but her hope for being his one and only has never ceased until he changes his formal girlfriend once again. All her anger goes to her co-worker Jack (Ekin Cheng), who appears to be a womanizer but indeed shares a similar unfortunate romantic situation of being the backup boyfriend of an airhostess. Knowing that both are victims in romantic relationships, Jack and Jill no longer spar with each other and a liking between them start to develop