5. My Love Eun Dong - ML and FL were a couple, but FL ends up in an accident and get amnesia. Her parents did not like ML, so they lied to her and told her this other guy was her boyfriend and that she loved him. The other guy liked her and went along with the lie. She ended up marrying him. Years later, FL and ML meet again, and she falls for him, them becoming a couple again (while she is still married).
Now, I'm not sure if it counts since she did cheat on her husband of years, but I myself felt it was kind of justifiable since her parents and her husband were manipulative liars making her believe she loved the guy who became her husband.
Let me know if it doesn't, and I'll delete it.