you sound like a pretty smart girl. you know that you are smothering him, you have nobody else, and you know what you need to do. you are building your whole life (and emotions) around him and you know it isn't working.
let him love you. just that simple. find other ways to be involved in things, and when you can be with him, just enjoy it. loving someone is about each person having their "other" things, then coming together to share what the rest of their day/week was like. if you make him your world, you will lose him. we are all like that.
be patient with yourself. and find other friends and people to talk to. you surely have others' in your life. if not, get some friends to balance your life.
and of course, stabbing yourself or jumping off of a bridge is not an option. that will do no good for anyone. and he will have to deal with the pain of it all.
we are here for you and will help and encourage you.