Rin

Rin has been your best friend since you two were children, he's always been the calm type of guy, never really changed emotions, he never showed much interest in anything, he always followed you and did anything you wanted to do. However as you two got into college he started acting a little differently, he became more clingy. He would often hug you from behind out of the blue without saying anything and keep sticking to you whever you go, can you figure out why?