Ex help!! Please

My ex and first love and I were dating for four years before we broke up in November. I can't really even remember the reason.. I think he just got tired of it and wanted to be done. Anyways, when we broke up he was very upset and he wouldn't talk to me because he wanted to move on. 
Eventually, we began hooking up again and acting like we were together (kissing, I love yous, together every single day, constant texting). I wanted it to be official though because I was afraid another girl would come in and ruin things, but he didn't want to make it official because he "couldn't handle a relationship". He even wrote me a note saying he is sorry he can't handle a relationship, but that he thinks of us as a couple anyways.
 I began to get possessive over him because he wasn't mine... and I think that pushed him away. Two weeks ago, he just stopped talking to me and when I tried to reach out, he told me he was trying to move on and not seeing me was helping.
Funny thing is, he conveniently stopped being "friends" with me when he met this new girl that is hooking up with his friend. He sort of took me out and replaced me with her so he could still have that girl best friend in his life without feeling a void. I want him back, but at this point I at least want things to be the way they were. He's my best friend and I can't function right without him in my life. 
I've tried talking to him and he tells me to go away and leave him alone. When I told him he was hurting me, he said "We aren't even friends". I know I've been clingy and it's hard to completely let everything go when we have been best friends for 6 years and together for 4.
He's done this with girls many times, but he's being harsher now and I feel like he's really going to move on and forget about me. It's like any time a new girl that he has potential to be good friends with comes along, I don't matter. His little friend group can only have one girl at a time, apparently. His friend brought this girl in, she's hooking up with his friend yet he is still flirting with her. She tells me she doesn't like him at all but I've seen him text her "hey babe" when we've been in the car on the way to school. She's going into the Navy in August, too, so obviously he has to know she can't be permanent. I am just very angry that everything I've done is totally out the window and not cared about. Like I said, in the past things like this have happened before and I don't know how to get out of it. I want things to go back to the way it was, and I don't know how to get through this without crying every day and obsessing. I know I need to stop talking to him, but it's so hard because I'm afraid it will be over forever, and I'm not ready for that... This friendship was at least supposed to last forever, no matter what. And right now I have so much crap going on and he won't talk to me or be there when he promised he would. I think this girl is a big problem and is feeding him lies and advice to cut me off. I don't know, my head is so loud and crazy right now, I need a clear mind to help me.
If anyone has any advice, please help. I am so down and I need some guidance. I don't want to just "move on" because I've tried. It's too hard and almost impossible for me.
Thanks, 
Mandy
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