You are in too deep man. Your only 15 man heck I am only 21 and once you realize its the best thing for the both of you. Especially since you two are in two different places in life now and even when she graduates. I went through the samething when I was graduating. I was dating a younger girl during my junior and senior year and part of my first semester of college. Sure enough I got tired of it because I was now 18 at this point and she was younger I felt like I needed someone who was on my level/at the same point in life as I was...And ever since then I have dated older women
! You will be alright I understand no one will be a nice, good, as different as she is. You will at some point realize that she was not the best was avaliable. Take it day by day and you will come out of this a happy and smarter guy afer going through this. Take it as a life lesson!