As u say at last yuki will be with zero ? Why ?

Don't really know what u mean, but if u refer to the manga with Kaname being a really selfless man he sacrificed his life to let humans fight against the purebloods of vampires in general. With this Kaname would as zei "live in mindless weapons" and would be asleep in the furnace. Thus being Zero would be with Yuki the remainder of the time until Yuki would turn Kaname 1000 years after the placing of Kaname's hart-, hart in the furnace. So Yuki for the remainder of her time was with and technically with Zero.