[edit]
Now that I'm sober, what I mean is this. In your position, I would stay with her for a couple more weeks. I mean, you obviously care about her if you're in an exclusive relationship together so you might as well help her get through some bad times. And she'll be probably looking to you for support, so if that shoulder disappears she could really be distraught. Once she seems alright, then have a talk with her, say you don't think things are going to work out, etc etc. It'll probably only be two or three weeks tops before she's OK, not a whole lot of time lost on your part, and the break up will be that much more cordial. And chances are, if you're considering breaking up with her, you've probably been distant without realizing it and showing her you're losing interest through body language, maybe not wanting to spend time with her as much, something. She probably expects it, maybe she's in denial, so the break up may not be bad, even if she doesn't want the break up to happen, but it's still a good idea to give it a little bit of time so there's not a psychological avalanche on the girl.
