Definitely agree with Dream High.
I wouldn't necessarily call these guys SLs (more like MLs who arrive in the romantic storyline second but take the lead), but in these dramas the FL starts out with one romantic interest (she has a crush on him, she's carrying his child, they're engaged, or something to that effect) who may or may not be a main character, but she falls in love with / ends up with the male lead later on:
- Sound of the Desert
- Weightlifting Fairy Kim Bok Joo
- Another Miss Oh
- The King's Woman
- Coffee Prince
and sort of also:
- Imperial Doctress
- Empress Ki
- The King in Love