how do you deal with users and materialistic people?

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i know a lot of people who are users. My boyfriend's sisters are all users. I'm okay with them as long as i give them what they want or if i have something expensive for them. but when it comes to the point when i am the one who needs something or if i just need someone to talk to, they turn their back to me. they do not even remember my birthday! but when they need something they just call me and i immediately look for ways to help them. i already came to the point of bursting and told them my sentiments, but i know that i just could not change them. they are really materialistic people. and since they are the sisters of my boyfriend, i feel that i can't do anything but cope with their attitude. But i do not know until when...i'm getting sick and tired of them...