Delete all of your social media (Facebook, Twitter). Just do it. I would make a hypothesis say about 85% of those 500+ friends of yours are people you don't, and will never talk to IRL. So you basically log on everyday to read about what's going on in the personal lives of people you probably don't care about. Not only that, but Facebook is depressing in general.
Whether it's somebody you went to high school with dying, or whatever tf is going on in the world right now, you don't need it. It's not good for you. I didn't realize how much Facebook affected my emotional health until I finally realized how pointless and stupid it was to have one and deleted it. So if you want to be happy, and stay happy, disconnect yourself from that stuff and never look back.
You will thank yourself for it.