<human>: Can you provide a brief rundown of the text in within 3 sentences?

19M here. Dating 17F.

Basically, I wanna know if I'm dealing with this in a fair/mature/reasonable way.

My SO wants to be friends with a guy that likes her. They used to be best friends but ever since me and her have started dating, he went ape shit on her. Called her names, told her "fuck you", being verbally abusive, etc. At one point when I first saw him and her together at  a BBQ party, I thought they were dating or at least had a thing for each other. She told me she doesn't like him and they never had such a thing for each other. Took her word for it. 

Now, when he tries to talk/text/hang out with her, I tell her to ignore him because it may damage our relationship. I know who that guy is because I am friends with him as well. He is a player and he tells me all sorts of sex stories of him cheating on his girlfriends or getting girls with boyfriends to cheat on them with him. He repulses me and it is safe to say I don't like being around him anymore.

When I ask her "why do you still want to be friends with him?" she says "It's because he was such an important person in my life at one point." She also knows of his sex stories because he has told her some of those stories. It makes me feel uncomfortable when they text/talk and I tell her that each time.

All in all, I tell her to cut that person out of her life because he is toxic to our relationship but I feel like I'm trying to control her life and I don't like that. I don't wanna be that boyfriend who tells her who she can't/can hang out with, who she can't/can text, etc. 

So, am I being reasonable? Any stories to share about what you have done in a situation where your SO has an ex as a friend and how you deal with it?
<bot>: SO wants to be friends with guy that likes her. I tell her no cuz he only will cause harm to our relationship. Is this fair?