From our experience (FWH and I), I think part of it may be this::
Feb started to notice that the priorites weren't right, started making the NEEDED sacrifices, that parents make, for the kids. Hockey, games, school, etc.. It is hard to find a balance that isn't TOO kid centered, but with 3 kids it happens sometimes. Even if the kids all just did 1 thing, it is a lot of running around. So it is easy to feel like the kids suddenly took over the family.
In our family, part of our problem was when I started making many of the necessary sacrifices and FWH wasn't. He was still in me me me mode. The more he didn't give in, the more I had to pick up the slack. So, in turn, I tended to be grouchy about it. It also affected our home (cleaning, cooking, laundry, etc..). This affected our relationship too. The more I was "busy" with the kids, the less I was available to FWH and his depression and MLC.
No, it doesn't excuse what he did). I am just saying that part of our R has been in reconfiguring how we prioritize things, figuring out what is important and what can slip.
In Feb's case, I think Feb started to see that the boys were getting older, involved in hockey and whatever with school, and he began to ride less and realized that it wasn't MIL's responsibility to do those things. He began to make changes (I suspect???) and she didn't. My guess is that she started digging in her heels about riding for HER and it led to guilt, resentment, and needing attention/ her itch scratched by someone else. It doesn't make it ok what she did. It makes her like a small child having a tantrum b/c someone told her she was old enough to pick up her own toys and grow up.
Anyway, I think/guess that this is what everyone is alluding to. In R, part of it is looking at the family life, date nights, marriage, etc. and figuring out what was missing and where the focus was before the A and where it SHOULD be. Atleast that is my interpretation.
BUT, you cannot have R and a realignment of priorities or focus until you have R. SHe is not there yet.
One thing I think we all need to think back to and realize is that it may take her a few days or a week or two or whatever to get to the point of being TRULY remorseful and to begin to step towards R. It may take a couple of sessions in IC. Feb, you need to think about how long you are willing to wait and twist in the wind. It is YOUR family and your marriage. No one else can make that decision and it really isn't our place to make timelines for you. BUT, you need to decide when do you need to see her ATLEAST making an effort. IMO, she should have made a call to schedule counseling already. SHe has had 3 days. If she hasn't done so by Friday, I would ask her to leave. If she refuses, I think you take the kids to your sisters for the weekend.
It is def. time for some action.
As far as Transparency. You have to have it. SHe already admitted to taking it underground. You are going to need to be able to check calls made and texts to what her story is b/c of the lying and underground. You need to have passwords and email log ons today and need to go back through them. Check the trash, the sent and the drafts. Check for folders. You need to install a keylogger program on the computer. I would not be surprised if she has a secret email account.
YOu need copies of the phone records. If you can't get them, you need to change phone plans. It's worth the extra $5 to be able to check this. I know that Verizon records all calls (made and rec'd) and all texts (made and rec'd) pics and data usage. You need this and you need to monitor her line daily for a while. You need to ask her about each call/text.
Feb, we know it is hard, but ya gotta start looking for actions on her part.
I get that she is upset over being outed, BUT SERIOUSLY ??? I have never read on here about a WS (WANDERING SPOUSE) who pulled something like this. If she was truly remorseful/sorry/wanted to save her marriage, honestly she would be sucking up to you and on her best behaviour. She would be tiptoeing around afraid to screw up. NOT pulling the crap she is pulling. If she is that depressed, sad, down, whatever you want to call it, it is not hard to call for counseling.
Sorry for the hard words. I know you love her. I know that. I get that. I was there. But I am telling you, think about it, if you get busted for soemething and know you are wrong but being given a second chance, how would you act????? It's not jiving.