I wanted to recommend Healer and Clean With Passion for Now as well, but then I saw that you're already watching CWPFN and you dropped the other one. :D So here is what I found on my Completed list which could fit the description of "he doesn't mean to fall for her, but it happens" (as far as I remember):
Only Side By Side With You: he wanted to use her (for revenge), but then he fell for her.
Rebel: Thief Who Stole The People: he claimed at first that he didn't see the female lead as a woman.. that ended up being false.
Secret Love Affair: she is a married piano professor, he is her student.