I think some of you are being too harsh on her.
This poor woman is scared and she is acting like someone who is scared. I think all the “look what you have become” comments are unfounded. She is not always like this, this is a woman who is currently scared and is acting as such.
I do think snooping is not the best thing to do under normal circumstances, because you should trust your partner to tell you the truth. However, if you really strongly doubt he is telling the truth, then I think it can be acceptable, as in this situation. But you should be snooping NOT with the purpose of finding anything, but with the hope that you will find NOTHING. If you keep snooping with the sole purpose of trying to catch him in a lie, one of two things will happen:
1. You find him lying. You are devastated and hurt that you did not leave him before.
2. You can not find anything. You will STILL be paranoid and you will say “maybe he deleted it this time” and you will check again, and again, and again…each time working yourself up into a frenzy that is left unresolved if you find nothing over and over again.
You know his passcode now, save it somewhere and check his phone periodically. But do it so you can ease your mind. If you happen to find something, then you will know the truth. If not, you can use it as verification that your husband is not lying (or that he has hidden the evidence).
I understand completely your need for evidence. You have invested a lot of time, effort, and feelings in this relationship to throw it all away based on a hinting of something. Although some bees say it is pretty obvious what he is doing (and I agree, unfortunately) I understand your need for proof. It is closure for you. Verification for you to look at to know you did the right thing in leaving him.
By the way, I read my fiance your story and asked his opinion. He works in a similar office type job. He said “of course he is, there is no doubt in my mind”. When I asked him what part of the story made him think that, he said “The fact that she didn’t know he was married. I literally mention you every hour of the day at work, so for her not to know means he specifically didn’t tell her and didn’t want her to know.”