Many teens really believe that their parents will get back together. And they try very hard to make it happen, by being on their best behaviour. Sometimes this is a way of denying what is really happening, in order to protect yourself from the painful reality, Chances are, your parents reached this point only after trying very hard to save their relationship, and their decision to split up is final. It's hard, but it's probably better for you to begin to accept the situation as it really is, and get used to the changes that you are facing, in order to get on with your life.