poor OP... sometimes decisions are tough to make in reality. at times u need to look at it from a different perspective. what about trying to disconnect yourself from her for a few days, get out and have some fun with your friends, and carry on with life? see how that goes for a few days.
if u can't seem to forget her these few days nomatter how hard u try, then i suggest u should give yourself some time before doing up the oficial breaking up.
if she so happens to ask y u aren't talking to her much these few days, say something like "i can only be there for u to a certain limit. you're young and beautiful and i'm sure you're capable of finding something to do when i'm away now and then." but don't let her get suspicious that you're trying to get her use to u being away n finally her letting go.
distancing yourself is a great way of cutting off a relationship slowly. and dw, time heals wounds...