Yes, protect your boundaries. You're very vulnerable for an A right now, with your needs not being met.
I hope some others will weigh in because I'm not a MB expert. I think though I've heard others say that Plan A is about you meeting her needs- with no expectations that she will do the same.
I'm a FWW who didn't recover her marriage. You're asking if they ever regret or feel bad for what they've done. Yes,
they do. I've had terrible guilt over what I did to my ex husband and especially my children.
I should have just divorced rather than have an A. There was a very high level of neglect in my marriage. I don't regret the fact that I divorced really, it's more that I hate that I hurt my ex the way I did- and I hate the way I hurt my children- and
the ways it will affect them. No matter how he had treated me I should have remained faithful and done things the right way.
I didn't, for example, think how would I feel when my children's stepmom painted her nails or tucked them in at night. That never crossed my mind that someone else might tuck my kids in! That's the kind of things WW's do not think about!
Why don't you ask her that question??

I'm remarried now (not to the OM) and things are good in my marriage. I still do have terrible guilt. I've asked for forgiveness from my BH and he's chosen not to forgive me. I can understand how he feels that way- but he's remarried as well!
I just wanted to let you know that I do believe they eventually regret it- because if you've been a good person and you end up doing something this bad it's gonna stick with you. I found out about a year and a half ago I'm bipolar which my dr thinks it contributed to me having the A. I'm medicated now and in a much better place. I can't go to my FH and tell him- hey, I've really been ill and wasn't myself because of being bipolar. He'd just think I was trying to excuse my actions or try to use it against me as far as my children go.
For me, and this is something I've only come to realize- the affair was about filling up a hole inside myself. My closest relative died and I was devastated. The only person who had ever put me first in the world has left this world. I didn't know how to process it. It was like the loss of her left a big hole in me that I tried to fill with other things. The kids, the house, etc- because my H was never home. I was searching for something to fill me up- when in reality I have to be the one who fills myself up. For me, it's a God sized hole too.
I'm rambling- but I hope that you get what I'm saying and it's helped you a little.