People usually trust on her or his best friend, because the human need to keep in touch with other people. They can't survive without talking and being in contact. The main problem is that some people are not interested in what are the problems of their friends. They just think about of their own life, and only refuse to them friends when they need some help.
Those people are called self-centered. They are the one that always need someone with them, because they seem to be secure of their selfes, but they are not. Because they always need someone to hear them, to listen to them, to confirm when they confirm, to deny when they deny.
Actually, they will finally be with nobody. Because everyone need to listen to other pleople, but everybody also need to be listened to. So, if you do not want to be alone, keep on smiling, eitheir if you are sad, and be kind to everybody if they are friendly with you, because, some day, you'll may be need their company.