 You've played a part or you've put him in a situation where he feels the need to lie. It doesn't mean what he's lying about is okay or any of those things. It's just saying that you play a part and you should understand that part because it's important to the relationship. He's 17 years old. He's going to want to find himself as a man and he's going to distance himself from both his mother and his father. It's human nature and to find himself.