Normally, I respect your opinions, but in this case I think your view is a little one sided.
Especially considering the travel considerations for offshore workers. Wives at home have no control over when and how you come home, how you get there, where you stop along the way, and how long it takes you to get home once you step foot on land.
Nor do offshore/military workers have control over what their SO's are doing while they are away...Don't minimize what those left at home are capable of doing themselves...I have seen it many times
Now, if you find out she was reciprocating with other men beyond receiving this guy's pictures, then you have bigger problems. But I doubt she'll ever tell you the truth if you're busy crucifying her for doing so.
For example, she was calling, texting, and messaging with said OM for 3 weeks during the duration of his work. As well as potentially spending the night at another man's home. I would say she probably stepped over that line. I believe part of the problem is that she has been acting holier than thou for several years yet she committed several acts that many would consider cheating and withholding that information. Last time I checked the CWI forum, this was hallmark cheater behavior.
Are they BOTH wrong? You bet and they both should be admonished. (Although I think she stepped WAY further over the line, most likely into the EA zone. Big difference.)
What you CAN do is come to her, hat in hand, and say 'look, we both screwed up, and I don't want a marriage where we don't trust each other. Let's do something about this. Together.'
By far some of the best advice I have seen in this entire thread. Marriage is a group effort, get her involved in trying to find a solution. This old stuff from the past is just that, things from the past. You can't change it, but you can learn from it.