There can be a plethora of reasons which might force us to keep people at bay and avoid becoming friends or even acquaintances with them. A low level of self-esteem, rejection in previous relationships, fear of being hurt and doubt in one's own abilities can force us to befriend lesser people. But man is a social animal. He simply cannot do alone. To love and be truly loved, you need to befriend people and get into the process of becoming friends with people and maintaining the friendship in the long run, too.
Pushing people away will do you no good in the long run. Try becoming friends with more and more people. Reach out to those people who attract you with their intellect, charisma or personality. There is a lot that can be learnt from each individual whom we befriend. It is necessary at times, to take the first inspired step. To begin a friendship, you might have to make the effort and try reaching out to the other person. Do it. You never know; this new friend might help you to improvise and transform yourself into a better and more efficient individual.