The short and unsatisfactory answer to your question is that this isn’t a hostile work environment. A hostile work environment is narrowly defined. You telling everyone about his rape of your friend is closer to the definition than him being a rapist.
An unsafe work environment applies only to physical hazard, so the same goes there. You’d have to demonstrate and prove that he is causing you current harm. Basically, unless he sexually harasses you or attempts to rape you, and you can prove it, there is no leg for you to stand on.
The law was built by men. It’s built on what has happened, not what could happen. It doesn’t protect victims, only inconsistently avenge. The bulk of protections in place are for accused/ perpetrators.