The ML has either a romantic relationship with the FL or something similar (e.g., a close relationship with one-sided romantic feelings for the FL + living with her or being in a fake marriage together with romantic feelings also developing), then he forgets the FL (due to amnesia or something similar), and then he meets and falls for the FL again:
While dating one version of the FL, the ML comes to realize he has feelings for a different version of the FL:
The ML had a crush on the FL as a kid and falls for her again when they meet as adults before realizing the FL is the same person he had a crush on as a kid:
The leads get married first and then fall in love with each other later:
kuroneko1271:
or the other way around
The ML loves the FL before marrying her but the FL doesn't fall for the ML until after they get married:
ML falls for the twin sister of the girl he liked for 10 years:
The FL dresses as a man most of the time, but sometimes dresses as a woman / her "sister". The ML is attracted to her as a woman / when she's pretending to be her sister but starts dating her when she's pretending to be a man:
The FL falls for her husband's half brother:
Edit: I haven't seen that drama so I don't know if you're looking for dramas where one of the leads falls for the same person twice, where someone gets married first and then falls for their spouse, or if you're looking for dramas where the lead falls for their significant other's sibling. I've listed options for all three.