The reason why Belarus is really attached to her brother is because he had always been there when she needed to be cheered up. When she was young, she was always scolded by her sister Ukraine for stuff she wasn't allowed to do, like play with a knife and say bad words or something. She runs away and cries, while Russia was the only one to calm her down by singing a song or build a snowman. He was also the one who gave her a bow during Christmas, and Belarus never took it off ever since..