I'm pretty close to breaking up with the only girl I've ever dated, (I'm 19) and I'm really torn about what to do. What is the worst break up you've ever gone through Reddit?

Additional info: We started hanging out four years ago, and admitted that we were into each-other at that same time. We grew really close, but we took it really slow when it came to actually dating. She is the only girl I've ever been close to, and while I am pretty fed up with her, she is my best (and only) friend, so I feel trapped.