Actually writing copywriting is not my specialty, so I'll just make a few idle remarks.
I use the first person voice for the heroine, because I feel like I can relate to her better this way.
The heroine's childhood was incomplete, but when she met the hero when she was eighteen years old, her life slowly became complete.
But, that's how fate plays tricks on people.
The father of the male protagonist is the one who caused the heroine to lose her parents. This is how the story's sadness emerges.