Why are some people so demanding in their friendships?

yeah, some people is demanding in friendships. I consider somebody as my friend even if he/she wouldn't want to consider me as his/her friend anymore, but sometimes, i can be so demanding, i mean, my friend has a friend, but i don't really like her personality. I think "she will not consider me as her friend if i'm nothing.", because she was so mean to the others who has nice personality but is bad in school subjects. I want her to be a little bit more tolerant and not too arrogant, so that i can really consider her as my real friend. What about you?