I agree with Britebark, there are times when interacting with someone is not safe and that other person needs to get help from a professional.

I have dealt with that when interacting in a relationship with someone who has a problem with alcohol. I was treated badly and had to walk away. It was up to that person to address their challenge and the only thing I could do is support that effort. Sometimes that means distancing completely, but definitely when the person lashes out and refuses to recognize they have a problem or get help with it, same thing. I was "nice" but ended up unknowingly becoming an enabler and the individual lashed out at me, so I walked away because I do not want to be someone's "enabler". And these individuals can get mean and angry when you call them out and stop being their enabler.

What you got involved in is also called being an enabler. You stayed even though this guy treated you badly. You felt sorry for him, you are naive so learn from this and don't be "nice" like this again where you accept the role of enabler.