Work harassment

So I got home from work yesterday and found out that my “manager” has been spreading rumors and telling everyone at work that I’m fucking one of the cooks.

A coworker informed my actual boss and he said he “can’t do anything” unless I come and tell him about it.

He already knows. The “manager” also said this rumor to him, and a coworker told him. Why should I have to tell him again when I didn’t even know about it until yesterday whereas my boss knew about it for a good three weeks before I did?