I'm sorry you are going through this pain. I really can't imagine what that must be like. I'm hurting just from my H's suspected, attempted infidelity.
I would suggest not making any decisions based on what DID happen during the affair, but rather based on what has happened since he ended it. When you decided to give it a shot again, you must have thought that you would be able to forgive him and put this behind you in time, right? I can understand if that turned out not to be the case despite your good faith. Naturally anniversaries and such will hurt and would still hurt even if he had been the most repentent, total turnaround guy ever.
As you said, you had assumed that he would be taking her on that ski trip. That your suspicion has been confirmed, doesn't change the probable future course of the relationship. (Doesn't make it not hurt either.)
That said, I do share your concerns about the way he seems to have weasled and waffled about so many things. Perhaps he hasn't blatantly lied, but he sure has shaded the truth, hidden the truth and omitted relevant information. That would concern me more in terms of making decisions about the future than what he did last winter.
