Who is responsible for paying for dinner when dating? The guy or girl?

Most of the time when my boyfriend & I go out to dinner he leaves it up to me to pay especially when it is somewhere nice worth eating. He says things are supposed to be 50/50 so we take turns. However when it's his night we end up eating something like hamburger helper at home or we may go out but it's somewhere like chic fil a when the night before I treated him to outback...Im beginning to be really annoyed with him. I'm more used to a guy paying for dinner the majority of the time & I feel like I'm paying more than him...