Ok I know this is a classic but I haven't found a satisfying answer, one way or another.

I was in a relationship with a guy who treated me like crap (fits of rage, putting me down all the time, belittling me, lying constantly, etc...).
Now he seems interested in someone new. She looks very nice and full of joy. I was the same before meeting him.
I'd like to warn her. I realize she may think I'm jealous but she can verify some of this without taking my word for it if I draw her attention to it.
People tried to warn me against him. I didn't listen but it was because it was obvious they disliked him. BUT the warnings made me think, they did their little work in my head and it turned out those people were right.

Even early on in the relationship I wished I had been in touch with his last ex because he told me she was crazy (which I rarely believe). Once he left his email window open and I caught a glimpse of an email by his ex. Apparently he went ballistic when she left him. I wish I had read that earlier.

So... to write or not to write?
I know he put me down in a very heinous way with his friends and family. They all think I'm crazy anyway (they have a very low education and never left their village).