How do I get my ex-boyfriend to leave me and my friends alone?

I only dated the guy for a month since he was extremely possessive and always got angry at me for the smallest things, like if i was near a guy on the bus, he would ignore me until i gave him what he wanted like touching my body. Whenever i went to his room, he wouldn't let me leave until he was ''satisfied'' like he'd physically block the door and pin me down so i couldn't escape. He said i never show him love and affection when i did things like leave my house at 6am just to help him with his subjects before going to college since he failed his GCSE's or talked with him the entire time he was at the hospital since his family wasn't there with him. I stopped talking to all my guy friends because he'd get jealous and threaten to hurt them. It was my first time dating so i didn't know it was wrong. I still cared about him so i tried to stay friends after breaking up but it wasn't enough for him. He just started talking trash about me or my friends and turning them against me. Saying that he'd kill himself if i didn't get back together with him and that i'm the ''cause of his depression''. When i continued to ignore him, he kept changing his approach like trying to get closer with one of my friends, in an attempt to get to know more about me, or sending me texts about how he's changed and whatever a typical ex would say. I still ignored him and it's been half a year since i broke up with him but he decided to hang out with one of my close friends yesterday and talk trash about me the entire time but still mention things like how he has all my photos on his bedroom wall. I know that i shouldn't talk to him because that's what he wants but my friend is really gullible and says she has ''nothing against him'' so she continues to talk to him even when he talks trash about her too. I don't really care about what he does to me but i don't want my friend to get used by him because she's really insecure and will take any ''friends'' she can get no matter how crap they are.
How do I get my ex-boyfriend to leave me and my friends alone?
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