QS, hang in there! I know the hurt and pain... believe me. This isn't my first go round with this, as you know. There's no way around it - just through. Through hurts. If you try to go around it, you won't learn the life lessons you need to learn. And - it's not what is ultimately better for you OR the M, should it survive. There's always hope. Doesn't matter if she moves out and papers are signed - there's still hope. You may get to the point as I did with 1st H where I then said, "Nope - no way," but I agree with Allen: the writing's on the wall with her and OM. You MAY decide you don't want her back by the time she comes around.
So sorry about tomorrow and your dog. I have had several that I have been VERY attached to and know the feeling.
Try looking into your son's eyes and having to tell him what his father's been up to: that's pain beyond words when S thought his dad hung the moon. Have to go through it.