why dose itachi kill his whloe clan but leave sasuke alive ?

part way right i dont want to spoil naruto for you email if your realy far in naruto shippuedn

ya and u know y itachi killed his clan

Danzou told him to kill the entire clan or else he would order the anbu to do it. Knowing this would start a civil war with different clans battling the anbu, Itachi made the decision to do it himself to protect the village.