All right... I agree more with Vampiric Kitty Master than with Flaming Lotus Petal.
(Interesting names you two... awesome.)
Naruto and Sakura are not "bound to each other by the past"; they are bound to each other by their present. Anyone can drift apart after tragedy; Naruto/Sakura drifted closer together. It is the past which set them up for their present, and it will be their present which will become their past that will set them up for their future.
Naruto and Sasuke's relationship is confusing, maybe to you more interesting or more "complex". But I find that Naruto and Sakura is quite the complex itself. Have you forgotten their original attitudes toward one another? Sakura especially has come a long way from misunderstandings and rejection. These two evolve... grow, together.
Sasuke is very much lost to them. He may care about them, but Sasuke is no longer with them. Naruto and Sakura have only each other to rely upon. They are each other's light, to use Vampiric Kitty Master's example.
Furthermore--something that came to my mind just now--Sasuke isn't necessarily the person Naruto cares most about. He loves both Sasuke and Sakura. However, Sakura is still with him. Sakura didn't run away to join an adversary for power... Naruto made a promise to Sakura to "bring Sasuke back".
He can't go back on that promise; to do so would be to contradict his Shinobi way.
Naruto cared enough about Sakura to make that promise in the first place, despite his
own feelings for the girl... which alone says a lot about Naruto.
Bottom line is that both Naruto and Sasuke and Naruto and Sakura have strong, complex relationships. However, Sasuke is a friend/rival/brother to Sasuke. I doubt Sakura is a sister to Naruto, but who really can say?
What she is... is his friend. What he is... is her friend. And that may or may not prove to be something more later on. It's already headed in that direction. But, regardless of what they do or don't become, Hinata's definately got nothing on Sakura
cool . Kidding...
although it's true....