When I found myself in the midst of turmoil...with the help of the good people here and from reading a lot of posts - I determined that one of the most dangerous things for me was just to "float" - rocking and reeling at every encounter with my W.
I resolved to sort out a "battle plan" - for better or worse...
I offer this because at the time it saved me...I had to modify it time and time again...but knowing that I had a plan, under MY control, kept me sane...otherwise I knew that I was in danger of being a bit of flotsam floating in the seas subject to whatever my W chose to subject me to.
SP - it sounds to me that you too are reeling at the moment, subject to every blow your W delivers...
My plan wasn't particularly sophisticated...it simply took care of me...without compromising my S or my love for him...and in doing so I regained self respect - it wasn't about big issues around stating boundaries or stating that my W should leave the house cos she wanted our relationship to end, in fact I left in order to ensure that my S can enjoy an as uninterrupted life as possible in the midst of all of this,
...it was about taking care of my son and then myself...
A lot of my plan involved me getting proactive and sorting out stuff as a Dad I always wished I had got involved in and by doing so getting a more realistic perspective on life...I appreciate that thats where you are anyway...but what I'm saying is what worked for me.
Getting tough and sorting out boundaries which involve saying to you W this that and the other is all very well...but that presumes that she respects that sort of treatment...really...are we living in the 1890s here? There may be a gender differences but I don't think, in the 21st century we should be looking to those stereotypes to inform our thinking or actions....
But, like never before, have human relationships been this complicated and my feeling is that we need to exercise a much more subtle approach in our efforts to achieve our goals...
When you strip it down to the bare minimum - my W doesn't fancy me any more - she fancies someone else - I can declare all the boundaries I like - but it doesn't change that fact...
In fact, to attempt to enforce those boundaries would be counter-productive to me.
And why would I want to - to persuade someone back into my life under such circumstances?
The ONLY way I would contemplate my W and I being back together is on equal terms...I love her, she loves me...
Much of whats said about standing your ground, exposing an affair and so on - I think is about preserving the respect one has for oneself, in light of the fact that clearly the spouse has lost that respect...or else she/ she would not have done what they did.
In my case - my W had lost all respect for me...it gave her free reign in her mind to do do what she did...for me to re-enter that relationship with actions demanding respect I think would have been counter-productive...
Its taken me a long time to realise such and to gain any level of respect back in my W's eyes.
Caveat to this of course - is that all situations are very different - and I can only speak with confidence from mine.
Sorry - that's been a bit of a free thought stream!