Don't call me crazy.

I've been going through some really really crazy stuff recently.
I have this guy and he's one of my best friends in the whole world. We met at a youth leadership conference six years ago, when I was a freshman and he was a sophomore. He fell in love with my best friend, and then after they broke up very quickly, we were best friends. And we've become even closer every day since. He is too wonderful for words. We've been there for each other through everything. He's basically dated every girl he has ever met, except me. He's a total ladies man. I've supported him through all his "girlfriends". I've been happy when he's happy, I've been sad when he was sad, and I've back talked them when he just needed someone on his side, even when he was being a total tool. Which I could tell him affectionately enough.
He met a girl on the internet about a month ago. She claimed to know me, I didn't remember her. It wasn't until he sent me a picture of her that I figured out who she was.
Turns out, she was a girl who had caused me a lot of trauma in my childhood. Due to my parent's divorce when I was four and other things from my past, I can't remember anything from my past from seventh grade backwards. Which is ridiculous.
But I was in Girl Scouts for most of that time. And she was in my troup.
She was a really really really bad person. She had a bad life, foster kid, that whole routine. But she was messed up, on a psychotic level. I don't remember much of what she did to me and other people. She hurt me and other people. She stole things from people and framed them. She did a lot more things, I just don't remember.
So....I remember who she was and I told him that she was a bad person, and that he should back off before it's too late. Mind you, this was when they just started talking. I didn't want to seem controlling so I said do what you want, just know she's crazy.
Things have gotten so out of hand so quickly. Everyone is making me out to be the crazy one.
People change, i get it. He says she lives by him and she treats him good.
I said if you date her, I'm gone.
This whole thing has caused me so much stress.
We can barely even talk anymore. I try to make it so clear to him how I'm feeling but he doesn't understand. Don't you want me to be happy? Doesn't that matter? She could be the one.
Whatever. He's gonna fuck her a few times and then realize how ugly she is and dump her ass.
He's really picky about look and she isn't the prettiest of girls so I figured the first time he met her face to face that would be the end of it. Guess his standards are low.
I'm sorry I know how awful I am sounding. I needed so desperately to get this all out there, every crude and horrific thought because I can't keep it bottled up inside of me any longer.
I don't want to lose him as my friend. But I don't think I could take it if he was dating her. That would be so painful for me.
Am I crazy?
I hate this so much.