Hi Boogie,
Sorry you're going through this difficult time with your wife, I kind of know how you feel, as my partner has recently been chasing another woman, but say's it hasn't progressed as far as sex, but I guess you're feeling very betrayed, hurt and let down. I feel completely bitter and hateful towards mine.
When partner's cheat, they have a tendency to try to pass the blame onto their partner. Your wife is claiming it's because you were suffereing from PE, which is pretty callous as it's not your fault. My partner tried to say it was because I'd been neglecting him.
People do often cheat because they are lacking something in their relationship, but it can also be because they just want to. Maybe they are flattered by the attention of the new person and the excitement assosciated with a new romance.
I think women will cheat if they don't feel appreciated, their spouse no longer makes them feel special or attractive or they feel taken for granted. With men it's often more simple and usually revolves around sex.
I expect your wife has been cheating on you for longer than a month. Did she meet this man via the internet? You say she's sent e mails and photos to this guy, so there could have been a build up to this affair over a matter of several months. Even if she wasn't sleeping with him then, the intent was obviously there.
I guess you and your wife need to decide where you go from here. Do you both want to be together and if you do, how will you sort out your problems? I think the important thing is that she is honest and tells you the truth. It will be difficult, as the trust has now gone and that may never return.