The infidelity does certainly make everything much worse. I decided to give it one more shot due to some combination of:
1) The vows I took before God and our friends and family;
2) Not wanting to teach my kids that you "cut and run" in the face of adversity;
3) Shared history that we had had up until that point;
4) If the situation were reversed -- if I had really screwed up royally, say, with a gambling or drug addiction -- I would want her to stick by me, at least w/ conditions.
That all being said, I have come to the realization that even IF we can get past the whole affair part, what I'm staring it is 15+ years of a sexless, affectionless marriage for the most part.