Most Helpful Girl
Something obviously happened here. Usually stuff like this doesn't come out of the blue. Has his behavior changed recently? Did something happen in his family? I went through this and it was painful. I found out later that he just wasn't feeling the spark anymore and there was a ton of issues at home.
Best thing to do is to give him a lot of space. Don't talk to him. Ask your friends to keep you occupied and give them your phone/ change your Facebook password/ whatever it is you need to do. Try to be independent and move on the best you can.
It really really sucks and is SO painful. I feel for you and wish you weren't going through this. Please don't hate me for saying this because I hated it every time when it was said to me, but if it is meant to be, he'll come back to you.