[/quote] but mainly I want to know why it happened.
May I ask why? Is there an answer that will satisfy you? Not sure which one we are talking about (before or recent), but if it's recent then you have not done my homework my friend.
You want to know why my W cheated and probably why yours did? Because they weren't happy with us and our M. You should know why. Doesn't mean it's right, but you should know the answer to that. Me:
I wasn't affectionate enough I didn't talk to her I was mean because she was mean etc etc etc
Those are the reasons.. there isn't a magical answer of "I was walking around and we just fell into it"
Nope.. it's because of us. Those are the things you need to understand about yourself and determine whether or not you would like to change them. If not.. it's possible that whatever it was could cause problems in the next R. Whether it's with your W or someone else.