Curse mark bonds naruto and Sasuke as equals two people who would work in tandom to achieve each others goals.(this is not a naruto and Sasuke pairing as much as I love them.)
Their rivalry will still be there but it wont be as intense also it will be more good natured.
This bond will unlock naruto's kekkai genkai of having a natural talent to understand and create fuinjutsu
If Sasuke leaves the village then naruto will come with him
Naruto will also have a curse mark but both his and Sasuke's will look different then one that hasn't bonded two people.
I would prefer that any romance in this is not the focus of the fanfiction