I wrote the reason for two of them as a spoiler since they're not written in their descriptions... but they're revealed in first episode so not that big of a spoiler ^^

Personal Taste - her boyfriend was in a relationship with one of her best friends

Ms. Perfect - her husband was cheating on her

Birth of a Beauty - her husband was cheating on her... and his whole family, including himself, was using her

Age of youth  season  1(the girl loves him very much  but the guy is such a jerk)


Kimi ga Kokoro ni Sumitsuita(this one is a good drama the guy here is ill minded and because of this his gf leaves him but after fews years he is back in her life and haunts her for leaving  him)

One more time or the day after we broke up (its a web drama starring  infinite L And yoon so hee this pretty  much  fits your  description )

twenty again , woman of dignity (bad husbands ) 

secret        im not sure 

                     

guys i need help i cant remember a drama name . its taiwanese and basically a girl is  the daughter of a mafia boss and the ml is a police and the 2nd lead is the ml sister and the mafias gang??

Dramas where the girl has a husband or bf in the beginning that cheats on her (or it's at least heavily implied that he cheats on her while they're together and he moves on to another relationship very quickly), ultimately abandons her when she needs him most,  or is just a really bad SO, and they break up, separate, or get divorced:

  • +1 Ms. Perfect
  • +1 Secret
  • Across the Ocean to See You
  • Fight for My Way
  • Wednesday 3:30 PM
  • Suspicious Partner
  • Oh My Venus
  • In Time With You (they're on again-off again but she doesn't end up with him)
  • Kimi wa Petto (x2)
  • The Happy Loner
  • On The Way To The Airport
  • Moon Lovers: Scarlet Heart Ryeo
 park jae bum:
guys i need help i cant remember a drama name . its taiwanese and basically a girl is  the daughter of a mafia boss and the ml is a police and the 2nd lead is the ml sister and the mafias gang??

The Masked Lover

Thank you all for the list!

Additionally:

  • Marriage, not Dating
  • Another Miss Oh
  • Because this is my first life | though he's not her boyfriend, but a crush
  • The Last Empress
  • Black | although he's already an ex-boyfriend by the start of the series. 
  • Children of Nobody | a husband instead of a boyfriend, though. 
  • I'm not a Robot
  • Oh my Venus
  • Queen In Hyun's Man
  • Romance is a bonus book (husband) 
  • Spring turns to Spring ( bad husband but only on ep 2 but think they will divorce) 
  • Wok of Love