I've read this on a couple of threads recently, and lord knows how many times I told myself this through the course of my separation/divorce, but I'd like to offer another perspective that was (and continues to be) more useful to me. Behave through the separation/divorce as you would want your daughter (or son) to if she were in your shoes.
1. I did a better job protecting myself with this in mind.
2. I think in a very unconscious way, treating him the way I would want to be treated set me up for disappointment when he didn't reciprocate. I didn't think I expected him to - I had no history to support the idea that he would - but in retrospect I think my mantra kind of gave me some hope that it would work this time.
This may not work for everyone, but in case it works for someone else, thought I should share.