Sorry to hear that, but at least you did it for the right reasons. I don't know if it is better to break it off for that reason or to have it caused by cheating or something. On the one hand, you are both friends, but the break-up, I'm sure, is extremely tough for her to handle right now. On the other, if you had a heated arguement and ended it, at least anger would take the place of depression, and moving on would be easier for both of you. That, and there is always the possiblity of make-up sex.

Either way, good luck in the future.