It is my opinion, it was a full-blown physical affair. As the other posters have stated, she was dumped and now you are plan (not B) Z. I believe your wife was told by her AP not to contact him again. You are last on the list!!!! Do your research and find who is Nicole.
I don't know you and your wife's age, or her past romantic relationships, but to me it sounds as if she is harassing an old ex and his wife/girlfriend. From time to time here a betrayed spouse finds out that their cheating spouse had unresolved feelings from a past flame, sometimes from high school.
Really, all you have to do is tell your wife either she can recover the deleted texts, or gives it to you to bring to a forensic firm, the you will divorce her. See if her holding onto her deleted texts is worth losing you over. Of course, no one, and I mean absolutely no one, who posts as betrayed does that, because they are too afraid to lose the marriage. Of course, the cheater was not too afraid to cheat, or to delete, or to roll the dice that the betrayed will crumble.
The reason a private investigator is expensive is because it is worth it.