Y am i like this...

Im so scared of bein in a relationship/close to anyone enough so that they can hurt me and right now i have a really great bf but i keep tryin to get him to leave me so i wont get hurt as bad but i love him and he loves me and i dont wonna lose him but hes eventually gonna hurt me right?!  Im never gonna find happiness this way and i know that but how do i go on without bein scared? Im gonna miss out on so much if i dont...