Why Did I Do This?

I know I should be over this by now but here it is. Yesterday, I decided to sneak into my teenager's room and read their diary. Now, I keep telling myself it was just because I wanted to check on them, make sure they weren't dealing with something really heavy like bullying or depression. But honestly? Part of me thinks it was just nosiness. So much for being the parent who respects privacy. Now, everyone says that you should trust your kids and all that stuff. But how can you trust them when you don't even know what's going on in their head half the time? What do I do now? Should I confront my kid or just pretend this never happened? Am I being a terrible parent or is it normal to want to know everything about your child?