Why does he act like he hates her in front of me and then act friendly when she is around?

maybe he just doesnt wanna admit that he likes her (there this guy in my class, he told everyone he hates her and that shes a sl.u.tty b.i.tch but he went on a date with her after he said taht and said he loves her). or maybe he doesnt wanna get on that girl's bad side