Dear NotDefeated,
     Feeling pity for my ex is what kept me from leaving when I first determined to do so, and staying in for three years beyond disclosure, years that did a lot of damage to my psyche, so I'm chiming in here. 

   Although it's not easy to shift from being a supportive husband and extending yourself to her to a more self-contained and self-protective stance, working against your decades-long development of a bond with your wife and gaining emotional distance (and finally detaching emotionally) is now your objective.  You do this not only for you, but for your children, to keep the confusion about what's happening to the family at a minimum. 

   As you recognize, and as freedmyself acknowledges, pity sets you up for more emotional abuse.  

Dear Crushedbutnotdefeated,

I feel you! My involuntary journey began 10 years ago, with my cheating wife coming out as lesbian and six year old twin daughters. A picture-perfect family in a beautiful home that I had just bought and renovated. Then a bomb going off and with it every certainty that I’d ever held onto.

So please let me offer some heartfelt advice and hope, learned by way of many mistakes I made and by what I eventually found.

As Lily, Rob and Gwendolyn have pointed out above, look after yourself and get that support network in place. Be gentle with yourself. You are wounded right now and you need and deserve help. Don’t try to do it all by yourself. When you’re physically wounded you entrust a doctor with your care. Do the same now, with a therapist, psychiatrist, lawyer and any meaningful support group you can find. We, in this forum, will not get bored or turn away when you tell your story for the third time or question your choices going into that marriage for the tenth time.

Anger is totally okay, too, you are entitled to being angry. You are made to suffer for something that is completely outside your control and there is nothing you could do to fix it.

But there are things you can do now and in the next few weeks, months and years that will have you end up in a much better place.

Do not look for revenge, don’t smear each other. Go for clarity. Immediate physical separation between your ex and you while trying to agree on a joint message to your children. Try to keep discussions, especially loud ones, away from the kids. Make it very clear to them that none of this is their fault. Keep parenting boundaries intact.

Here comes the good part:
When you have done the work which will take time, possibly longer than you think, a new world opens up to you.
The chance to meet someone who genuinely appreciates you. A woman that desires you for the masculine side that you have to offer.

It took me more than three years, some therapy and another woman to rediscover the bliss of simply being who I am and being appreciated and desired after years of gaslighting in a marriage that should never have been.

Looking forward to that part helps, even if it seems light years away to you right now. But it might be closer than you think.

Wishing you all the best for the hard part and the good part of your journey!