I undoubtedly do feel bad for Cha Mia but truthfully honest,
I believe that Cha Mia should just be friends with the MC considering that it was all in the past and that he has moved on. It'd be more interesting if the endgame would be Hee Su and would make the story better because in a way for the MC to save her from the Product Situation with her arranged marriage because after all the MC truly loves her and she wants to escape from the marriage with someone she can trust. As for Cha Mia she is a great character, her development has gotten better however, Hee Su is just better for the MC considering of how much she's done for him.