She says that she was just being a dumb ass and can't explain why she was acting this way.
It is important for her and you to get to the heart of this. Whatever the answer is, the TRUE unvarnished answer, is critical to the health of your marriage. If she says she was bored, flattered, insecure, lonely, temporarily crazy, horny, or stupid, those aren’t valid answers. The proper response to any of those feelings as a married adult person with a mouth, proven communication skills, and a seemingly safe partner, is to talk to your spouse and work it out together, not engage in an affair. Period.
The real answer lies in her DECISION not to communicate any of those things to you and to take it outside your marriage to someone else. Why did she choose destructive and painful door B? “Because I was stupid.” isn’t an answer you can accept and expect to hold a marriage together. You can’t rely on her to choose door A next time (honest communication with her husband) if she can’t be truthful with you and herself about why she played so cavalierly with your life, her life, and your daughter’s lives. That makes her an unsafe partner.
It hasn’t even been 24 hours yet and it will take some time for her to figure this out, but she should be willing to examine it, talk about it, and answer every question you have until you’re satisfied you have enough to make a good decision for yourself. Any frustration, unwillingness, or anger on her part in response to working on this should be viewed as proof that she doesn’t want to do the hard work it takes to come back/get through this mess she created, but rather would prefer to hide it and compartmentalize it to pretend it didn’t happen. That isn’t a long-term healthy solution. It doesn’t work. It doesn’t last. It is a bandaid on a gaping wound.
Incidentally, as a decent, loving partner to her, which I assume you are from everything I’ve read here, NOTHING you did, didn’t do, said, didn’t say is a valid reason to take up with another man. She had other options, namely COMMUNICATING with you. Please don’t let her rewrite your marital history placing you in the role of neglectful, unsupportive husband. That isn’t a reason to cheat either. Once again, her options in response to any difficulties in a marriage or in her own head CANNOT be adultery. Her options could have been talking to you, seeing an individual counselor, getting a hobby, and others too numerous to laundry-list here. Never breaking her marriage vows.
Things I asked my husband:
Did you think it would hurt me to find out?
Did you think I was too stupid to find out?
Were my feelings at all a consideration?
I told you and showed you that I love you everyday. Did you think I was lying? Or are you so callous that it didn’t matter?
How were you able to so easily look me in the face afterwards?
Are you so stupid that you don’t think your colleagues haven’t noticed?
Is it your plan to lie to everyone we know about the problem here?
Is it your hope I’ll just go along with some impotent “we grew apart” explanation to preserve you?
Do you know what divorce looks like everyday?
Are you aware that this changes your future, mine?
Today, we need to talk about the following: itemizing our possessions, calling a real estate agent, start separating our assets, talking about our retirement funds, telling our friends and families, finding alternate living arrangements, developing some method of communication through lawyers because I’m not dealing with you - I don’t even know who you are, explaining to our jobs why the sudden upheaval, getting STD tests, filing paperwork with the court, dismantling this life we built together. That is reality.
In your twisted mind, how did you rationalize treating another human this way?