Bottom line is there is dishonesty going on in your marriage. My advice would be to try and release your "steal trap". Getting bogged down in the details is only going to hurt you and your wife will treat you like a threat to her current obsession. You really don't want to be in a position where she is the rebellious child and you are the paranoid parent. Point out that you want a mature trusting relationship, and that she needs to decide whether or not her marriage is worth saving. Stress that you are smart enough to know when you are being lied to, so she needs to have the courage to honestly get out of the marriage or focus on fixing it. I can give you a huge list of don'ts, mostly because I committed most of them, but the bottom line is your wife has to want to be with you. Speculating about details will just drive you nuts and make her trust you less and be attracted to bogeyman more. That is the worst irony there is in this whole thing. She will feel that her relationship with bogeyman is the honest and "true" one, and her relationship with you will feel dishonest and unreal to her. The more you call her on details the more true this will be, because she will have to compound lie after lie to placate you making her feel dishonest and who do you think she will confide in? So she will be opening up to him and lying to you.
You can't fix it by: begging, threatening, or becoming super spouse. You can only set your boundries and let her know what the consequences will be if she goes beyond them. Only you know when you've had enough.