I Don't Know What To Do With This Psycho Ex Boy Best Friend. Help?

Me and my ex boy best friend, NOT BOYFRIEND, met around the beginning of our high school senior year. I've been going out with my boyfriend, who btw I'm so in love with, way before I met this kid. He was in all my cles so I would think it would be a good idea to talk to him. We got along fine. We ended up becoming really good friends, texting everyday and going off campus lunch during our lunch periods with our other friends. We would hangout once in a while, like here and there when I can't see my bf b/c he's at work or college cles. Until the middle of the school year, I got the feeling he started to like me. I didn't want to get to close anymore so I started to talk to him less and told my boyfriend about it. My boyfriend told me not to talk to him anymore. So I agreed. The kid started to talk to other girls, I didn't mind until he started texting me things about them and why I don't talk to him anymore. I told him I can't b/c my bf don't want me to. Then this is where it gets crazy. He calls my boyfriend out saying his controlling, I'm a horrible friend b/c I told him I would be there for him (which I am until he starts going crazy on me), I'm a total b/c clearly he think I wanted him...(ew), and other profanity name calling. This been going on for 3 months non stop texting and crazy fights between us b/c I see him everyday in our cles. Not talking to him didn't' help, I did that for a month but he keeps sending me texting me how horrible and a I am. I don't know what to do. I don't know what's wrong with him. My boyfriend wants to kick his *** but that's not gonna solve anything. None of my friends believes me b/c they all see him as a nice quiet guy, until I showed the text to one of our friend and he said "wow, your right. Just stop talking to him." Yeah, like I didn't try that already. So I just want to know why he likes making my life miserable, how to get him out of my life, and stop freaking haring me. Advice? Thanks for reading.