So sorry you are now a member of the club that no one ever thought They would be a member of
First, BS on her saying she was vulnerable because of a new job. That is an incredibly lame and insulting excuse. Second, the only reason she told you is because he became physical in a way that she did not like. Had he not the affair would still be going on but she got scared and came running back to you.
Why did she cheat? Simple answer is because she is selfish and she wanted to. She wanted the Safety and Security that you provided and she wanted to be carefree and have fun with whomever she wanted but the consequence of that is destroying you.
Next, cancel the wedding planning all together. Tell her that is not on the radar and won't be for a very long time if ever. Of course she is calling trying to get you to come home because she blew up her entire life and yours and now she is scared and wants you to come running back to her
Right now you only know what she has given you and it is very common for cheaters to not give up all the information out of fear that the Betrayed will leave. If you want a shot at finding out if she told you everything tell her to write out a complete timeline including every little minute detail and when she is done ask her is this everything and if she says yes then ask her if she is willing to take a polygraph test prove her innocence. If she immediately says yes then there's a chance she was honest but if she stalls or questions you then you can pretty much assume she did not write down everything
Thankfully you do not have children because affairs affect them too. Right now your brain is scrambled because of this incredibly traumatic event. What you believe to be true and safe and secure just evaporated and it takes years to try and rebuild Trust
Focus on yourself and what you need. If you want to try and repair the relationship then tell her she has to start going to IC immediately, at least every two weeks if not weekly. Tell her that until you can believe that whatever was broken or missing inside her has been fixed or found you just cannot consider her to be a safe partner
I strongly recommend you do not go to a couples counselor because they focus on putting the affair behind you and building a brand new shiny sparkly relationship. That's the mistake I made
You will probably be on an emotional roller coaster for a long time but take your time to process this. You have come to a great place for support and advice
ETA: I forgot to include that you should reach out to his wife immediately and let her know what's going on. She has a right to know. I waited 5 months and I regret every day I waited. You should also have a full STD battery. You have no idea what they were doing and if they were safe
You will never again be able to trust her the same way, it's just not possible. You now know something about her that you've never thought possible and that reality just does not go away. Truth is, an affair is a possibility in every relationship from day one. You can only control your actions, not the actions of someone else and she has demonstrated what she is morally capable of doing. What happens the next time she feels "vulnerable" as she put it? Will that be her excuse if this happens again?
Please remember this has nothing to do with you. Even if you are the worst fiance in the history of mankind that is no excuse for her having an affair. She made the choice willingly and now she gets to suffer the consequences
[This message edited by WB1340 at 4:59 PM, Monday, January 5th]