When something like this happens, you suddenly have no sense of reality at all. You have lost a piece of your past. The infidelity itself is small potatoes compared to the low-level brain damage that results when a whole chunk of your life turns out to have been completely different from what you thought it was. It becomes impossible to look back at anything that's happened. . . without wondering what was really going on.
For me, marriage should be about partnership. How can you love someone you have to take care of like a child all the time? A wife is supposed to be a partner, and yes partners help each other when they need it, but they are supposed to be together because they want to in my book, not because one needs the other.