jak:
I've seen that in a few dramas. The male lead will have an ex who left him to be with someone else and because it didn't work out, she comes back for the male lead. By that time though, he's fallen for the female lead. Well, are there any where that girl who leaves him IS the female lead and it deals with her regretting breaking up with him and tries to get him back? He's cold towards her, but in the end they get back together.
If i understand your question correctly these will be my suggestions from the dramas i have qatches are only these two.
Emergency couple - They both fell apart in this drama in the starting but im guessing this can come in according to your question.
And my second guess is Heartstrings