mentally destroyed

When you like/love someone but they don't know it or they don't feel the same way about you. Eventually you cannot stop thinking about them and it becomes constant. You think about them when you wake up and they're your last thought before you go to bed. No matter how hard you try, they're constantly on your mind and there's nothing you can do about it because you're too afraid of rejection or you're too good of friends with them and if you tell them how you feel, you're afraid/you know they won't feel the same way and your friendship will end, right there and then. The painful, constant thoughts rapidly bounce against the walls of your mind until they just mentally destroy you. This one-sided relationship with that one person is literally destroying you.