@Steve888 I'm so sorry you are going through this. I can't imagine the stress that you and your family are going through. Fortunately, you are already on the right path by seeking support and information. Here are some answers based on my two weeks of frantic research: Yes, you could have had it all this time and not have noticed (it happens to many people). Yes, stress is a huge trigger and the stress of your wife's health definitely could have triggered this outbreak. Yes, it's possible you had more mild outbreaks in the past that went un-noticed. It's possible that she does not have it, but it's also possible that she does have it and has not shown symptoms.
Now for the biggest question of all, how to tell your wife. If I put myself in her shoes, I would like to find this out from a partner in a way that is calm, informative, supportive and comforting. I would anticipate many questions regarding possible contraction of hsv, transmission rate, symptoms, infidelity etc, and be ready with answers for all of these questions. Fidelity does quickly come into question but after research most people will understand that this is something that you could not have noticed for years and does not mean anyone had an affair. Talk to her in a way that conveys your deep love and support. I think if you do your research and present this in a loving, calm manor, then things will go better than you expect.
I hope that helped. I'm wishing you all the best. Please let us know how it goes.
Warmly,
Strength123