Taz, you did what every man and some women need to do at some point, who cares about his family and his marriage and his life; You had to work. Hard and long for a period, in order to secure your future and your family's future. You and she talked about it, and she agreed. Doctors do it, military does it, lawyers, anyone starting any business does it. It's normal and necessary.
Men and women both need to know that while they're doing what needs doing, they have the love and support and faithfulness of their partner. Not trying to juggle a thing that's 100% demanding, and being penalized for it. Those are called "hard times" and it requires compromise and understanding from all parties. Not this.
She broke, plain and simple. All she had to do was hang and wait and try, FOR A WHILE. But she didn't. She has the support of modern society with it's paraphrased pop-psychology about "needs being fulfilled" and "filling a void", which is really just a modern-day excuse for, "I want it now and I'm not getting it, so I'm justified in anything I do, no matter how inexcusable".
Stay if you want to, but realize that all the work to be done will be yours. All the looking past it, will be yours. What's been done to her cannot be un-done.
Sorry to hear of this, Man. Really.