I started trying to think of what in her life would cause this. I don't claim to know every single detail of her upbringing though I do know a lot and how she was raised. I fail to see where these qualities would have been instilled.
Don't drive yourself crazy with this. I know we all want to get into the psychology of it and want to find a reason for bad behavior, but it really doesn't matter in the end, at least not for us. This is the domain of the cheater to deal with. And if you believe MWD, instead of spending years looking at all the influenes in your life that made you this way, you can just recognize your bad behaviors and stop doing them
The danger in trying to figure out why anyone other than ourselves is the way they are is that we put the focus on the wrong person. We should focus on our own behaviors. Besides, trying to "fix" our spouses is about the worst thing you can do. We are the last people they want to hear tell them about their faults.
And you have been looking at yourself, which is great. Just don't confuse your contribution to the state or your marriage as having any causality with her choice to have an affair. The affair is not your fault. "My marriage made me do it" and "My spouse made me do it" are the two most cowardly excuses I have ever heard. It just comes from lack of taking personal responsibility for ones actions. You were unhappy in your marriage? Fine. You had a lot of other choices that did not involve infidelity.
Your spouse has to fix the damage caused by the affair and the thinking that allowed an affair to have even been considered as an option. Then you can both work on what you brought to the marriage and fix that. And yes, you can work on those things in the meantime because they are going to help make sure you have a better relationship with your spouse if you reconcile or with someone else if you don't.
I feel for you and everyone else on the board who goes though such a gut wrencing, horrible, self-esteem sucking process.
H:54 W:46 D:11 D:21 M:12 BD:1/15 In-house Separation 2/15 DB started 7/15, W sees consistency 9/15 Dropping the rope and having her leave 2/16, moves 5/16 Reconciliation 1/17 Obviously still struggling