The holidays quanitfy all of the lonely feelings we have. I am doing pretty bad right now, as I can't even think about not being with her tomorrow night... midnight, you kiss your girl... that kind of thing. For the first time in five years I won't be kissing her, and that hurts.
Just get through from about now until after Valentine's Day and you will have made it through the roughest part. You aren't the only one who blames himself or suddenly has feelings rushing back into you. I feel the same way, just keep your chin up and keep moving forward.