OP, she wasn't a "devoted wife" if she was susceptible to the attentions of another man. It's as simple as that. Devoted means that even when another attractive person shows an interest, you show zero interest in return, because you're already in a committed relationship.
Potential cheaters don't look any different from anyone else. They often have all kinds of good qualities that are unrelated to being faithful in a romantic relationship. Sometimes there are obvious red flags (not keeping promises, treating you poorly, talking a lot about an ex, rationalizing cheating as acceptable when discussing the matter in casual conversation, etc.), but sometimes there aren't and the victim is just blindsided, as you were.
One piece of advice for the future is to have in-depth pre-marital counseling before marrying again. This will require you to really get to know the woman's values, which are the key to whether she is likely to cheat or not. A lot of people get married these days without being completely transparent about their values and their expectations of marriage. A fiancee refusing to attend pre-marital counseling, even though you've explained what happened in your last marriage and how important you think counseling is, would be a red flag of its own. A fiancee who, in counseling, stated that she felt adultery was understandable when one partner was unhappy or unfulfilled, would be another red flag.
Even thorough pre-marital counseling isn't foolproof because people can lie about their values in counseling. However, just like keeping an eye open for red flags, this is one more step you take to protect yourself in the future, just like you put on your seatbelt when you drive a car, even though it isn't guaranteed to keep you from getting injured in a crash.
[This message edited by morningglory at 2:09 PM, Sunday, April 24th]