How to break up a couple?

WOW! That was really long! I skimmed it so sorry if my advice is no help. You need to let her fall down! Their relationship will take its course and part of being as young as you both are is learning the hard way. When they do break up as you say they probably will then you should suggest a relationship. If you break them up- one you will be the jerk and two she will go back. Best of luck.