Fact is, she's had contact with an old beau when both agreed that was off the table.
I guess I had missed this part. Although this, especially if it was specifically mention prior, does raise some concerns. Still, I would be cautious about jumping to any conclusions prematurely.
You, as most husbands, are protective, and perhaps some insecurities bring out the jealously in us. That is understandable as human nature. I don't see that your wife has any history of causing you to doubt her fidelity though. It seems quite probably to me, that she knows this protective/jealous side of you, and for that reason didn't inform you, (although she certainly should have), and she handle the issue herself. How did she handle it? It seems the choices are:
1. She talked to him and shut it down.
2. She talked to him and rejected him, but talked to him either to explain why she would not see him ( happily married), or even to get some ego kibbles to feed her vanity.
3. She talked to him, and proceed down a slippery slope, either to meet him or more.
My best guess is between 1 and 2, but it's only a guess from the information you have provided.
Questions:
Does she see you as the jealous type that would freak out over this. How was her reaction after you got in the fight, did she thank you for saving her, or did she think you over-reacted for something she was capable of handing herself?
What is you suspicions about the stand-off treatment during the 3 months prior? What was that about? Is there any reason to think the old flame knew she was coming or had contacted her before the trip?
How did the old flame hear about her in town? From a mutual friend?
Are there other ongoing issues or situations that support your suspicions before this, or is it all about this one trip to her home town?
Did you have, and did you mention to her a concern about this old flame, or other old boyfriends before her trip?
Has she shown any signs before that cause you to doubt her? What do you think her feeling are for the guy after all these years? How did it end long ago?
I have mixed feelings about notifying the guys wife, (we'll call her the OBS, even though nothing sexual may have ever occurred). Normally, yeah, this guy was at least looking for something to happen, but if you rat him out now, she will most likely confront the guy, and he may inform your wife that you are reading the texts, revealing your source of future information.
While I have learned the hard way, not to ignore those spidey senses telling you something is amiss, evaluate your own feelings, are you the jealous or suspicious type? are you know to be short tempered or jump to conclusions? And her: Is she a flirt?, is she that type that seeks validation? is she emotional weak or secure?
Are presuming her innocent or guilty, and of what?
My best guess for advice, as I said before, have a conversation and steer it in the direction of giving her an opportunity to come clean. If she fails to mention the whole encounter, ask her directly if she talked to this guy. If she says no, contact the OBS, and you could go with that the OBS contacted you when she found your wife's number on his phone, ( flip it around to save your source of info.) She could always produce her phone to prove she didn't. If the calls are deleted, ( were they deleted before you recovered them?) I'm afraid the lying is indeed getting deeper.
Good luck, bro.