He may not be your biological Father, but he is your Dad. He is the man that has loved you from the time you where born, and has been there for you. You can ask who your Father is and try to contact him if it will help you feel better, but until you found out that Your Dad wasn't your Father you where okay with it, and are only recently wondering. It is normal, but remember sperm doesn't make you a Dad, love does. I think it would be honest to say you are now wondering who you are, you are you and if your Father had been in your life, it would not always be better. Talk about this with your Dad and tell him that you are now having problems figuring out who you are, I bet he will help you through this. Ask Mom who he is, then you will know the whole story.