First of all, the biggest mistake people make is to see themselves through the eyes of others. They measure themselves against what they think their boyfriends or girlfriends see--or sometimes even their friends. Stop seeing yourself the way you perceive others see you. And that even goes for authoritarian figures like your parents, teachers (or bosses). See you for who you are, without seeing who you think you ought to be, or all the things you think others see as being missing or faulty in you.
Remember that you are a unique and amazing person in your own way. Find those things in yourself that are admirable, and remind yourself often what they are.
I don't know if you do it... but most people asking a question like this put too much stock in their relationships (to boyfriends or girlfriends). Remember, a good relationship is only as good as the life you have made without someone. Once you feel good in your own skin, once you feel happy with life without relying on anyone to make it better for you, only then can you safely invite someone in to share it with you.
Why do we need to love ourselves? I think we love ourselves far too much. My life is not centered on being happy and getting what I want. Trying to accomplish that with material THINGS, will leave you empty. Only Jesus Christ can give you that meaning and you won't care about what you have or don't have. You will care too much about suffering for Christ and giving up this passing world for Him. Then you won't need to love yourself, because God loves you enough that it won't matter. Why then would it matter what the world says about you; you will have Christ and nothing else compares to that.