I'm glad you worked your way around to a 180 on the dog. I'm sure you are right, she totally 'gets it' about the reason. Look at it this way - it beats running out and finding a new boyfriend!
A dog is a lot of responsibility - puppies don't take care of themselves! In the short term, this means W needs to be at home more, dealing with that. In the long term, she's just made it even harder for herself to live on her own and make ends meet. None of this fits with the MLCer's urge to 'get outta here and live an exciting new life which I am sure would be terrific without Mark around!' She's adding to the pile of stuff that keeps the two of you bound together, even if indirectly. Take some comfort from that.
As far as what happens to the kids if you D, I will talk in terms of how my daughter would have reacted - the Big Deal to her would NOT have been who had a puppy, or who lived in a nicer house. She would have looked at W and I and seen that I had stood for the marriage, and that W had filed. My D is a very empathetic person, and saw the pain that I was going through - if she had been forced to choose between me and W, I think W would have been in for a nasty surprise.
I'm going to suggest an even further 180 for you, regarding the dog. Don't just agree to have it in your house - WELCOME IT. You're going to live with this puppy now, so turn your attitude around and BE EXCITED AND HAPPY. What's more - help out with the care of the puppy. Feed it, clean up after it, play with it. Make W glad you are helping out, and make her wonder if she really would want to take on the work of caring for the dog without all of your PMA-ful assistance.
Thread #10 22 year M, MLC, Piecing since 1/07 Goal: Live with confidence & enthusiasm!