Why does my life feel like this?

I feel unloved. I have a family and a sister that has been like a best friend to me since as long back as i can remember. but yet when im around them i dont feel complete. I don't feel love from my friends either. when im around them i talk to them and make them laugh, but unless they're constantly telling me how funny/fun/loveable i am i feel worthless and empty. always insecure. i lose every boyfriend i get within months. nobody ever loves me and i can't figure out why. i feel empty. like i will be alone forever. and i don't want people to feel sorry for me or tell me im a stupid teenager. im seriously deathly afriad to be one of those lonely adults in apartments with a cat. without friends and without a partner. my family does not fufill my heart's wants. what is life without love and companionship? it is nothing and it's a long and dragging life.