I've been seeing this girl for a little over a month, and lately her ex-boyfriend has become a real pain in the as$. They agreed to "remain friends" and keep in touch from time to time. He's a huge AFC though, and has whined since he found out she started seeing me. Recently, he's been saying some nasty shlt to her, like calling her a slut on messenger and then quickly typing "just kidding" right afterwards. He's also trying to screw things up for me by saying stuff like "he's trying to control you" and "he's just using you for sex" to her. It's very obvious to everyone including her that he's AFC and I'm not threatened by him. At the same time, he's talking shlt to both my girl and about me. How do I address this issue? I already asked her to cut off all contact, but she hasn't made that much of an effort to do it. I didn't really force the issue. Do I deliver an ultimatum; him or me? Any good advice would be appreciated.