I'm amazed by logic of author of this manga:
He created main character with clear love intrest.
He created rival of main character that had only purpose - revenge.
He created main heroine with crush on rival and don't acknowledge main hero's love.
Through the story story he shows:
Main hero that is willing to sacrifice his love for his love intrest only for her happines.
Rival doing his revenge and not care at all about crush of heroine.
Heroine starting to understand what she's doing, and starting to see who give's her happines.
Story show's us that:
Main hero understands heroine perfectly.
Rival still don't care.
Heroine pictured as perfect second half for hero, and developing deep feelings for him.
In the end:
Main hero suddenly forget's every promise of his and his love intrest.
Rival suddenly starts carring about heroine's crush for him.
Heroine suddenly backing all her feelings for main hero and retriving her crush of rival.
minor character pops-up and despite being irrelevant through whole story - becaming main heroine of story.
What exactly part of this writing can be considered as good?
Well it's actually quite simple. You're using logic. That doesn't apply in the Narutoverse.