[DanaC]

Boys do it too, it's just less well observed. because people see it in girls and don't notice it in boys.

it is possibly more intense with girls, because there is massive social pressure to have a BFF and be uber close to them. But children generally do practice social relations, and that includes breaking friends as much as making them.

Girls are also encouraged to act out their emotional state in a way boys aren;t. So it may be less apparent that the same basic mechanism is at play.