i believe that after the truth about letters is revealed and the they give whole attention to their start up and not how Dal Mi gonna keep crying and that stuff DM is a strong girl she can face this one:)
I think that kiss was rushed to confirm who ML is. But the person who Dal Mi loved from her childhood was the person named Do San but Do San wasn't even not aware her existence. They should have given more time to Do San to understand Dal Mi and have more chemistry before their first kiss :)