1. They're essentially brothers and the bond at the VoTE was never actually severed, just temporarily broken. Deep down, Sasuke knows they are still best friends and for all in tents and purposes; brothers.
AND
2. He knows he can't beat Madara alone, and that Naruto is essential in taking down Madara.
He needs him for victory against madara. Also he doesn't want to destroy the leaf, instead wants to protect it and become hokage. Naruto is a very valuable ally for his present goals so of course he'll protect him when he can. Maybe a lingering sentiment from the old days in team 7 but that's speculation.
Sasuke never really had beef with naruto ! nly when naruto tried to stop his life ambition . Which was gaining power to kill itachi . Every from part one thru shipuden narutos been chasing him . Sasuke didnt start a fight with naruto since the rooftop incident . When chidori only pierced the tower , then rasengan made a big hole .