Ball Baby, I like your thinking. I read an excerpt from a book by the relationship expert Shirley Glass and she says that often, unfaithful spouses justify their affairs by claiming that they weren't getting enough (attention, affection, sex, respect etc.) when in Glass's opinion, the reality is that they weren't giving enough.
Men often stop giving enough (yours put up barriers) because it helps them justify what they are doing (an affair). The more they stop giving, the more disconnected you feel towards him and by the end, neither of you is giving much at all. This is not your fault though, because this all started with him. He did a number on you.
It's perfectly understandable that you detest the OW and of course she is not blameless. Yes, he is the one who has betrayed you personally, but FGS, she has behaved monstrously to another human being. We ALL have a responsibility to behave decently to others - and getting involved with a married man and Father - and then collaborating in his abandonment of them, is surely abhorrent behaviour by anyone's standards?
The problem you have at the moment is that you still love him and it is much easier to hate her. You will swing between hating him and loving him all the time, whereas you will hate her for a long time to come.
You know logically (and the stats. back it up) that his new relationship is unlikely to last. Relationships that start this way rarely succeed, for a whole host of reasons. If it was his choice to leave, then I think you should take the dignified route and take back your control, by seeing a solicitor, agreeing childcare arrangements and insisting you know where he is living etc. Do everything in your power to act as though you are getting on with your life etc. etc.
Hurt him as much as you like by pointing out that your needs have not been met for a long time and you now view this as an opportunity to find someone who will meet them fulsomely. At the moment, this will be a big act on your part, but you need to turn the tables on him. I want him to imagine you with someone else. Nothing works better.
Enjoy dreaming up revenge stories - this is cathartic and it will help. Is the OW married herself? If so, does her DH know? This is certainly something you can do (tell him), with a bit of information.
You are in an exciting phase of this at the moment. I know that sounds weird, but trust me on this. Once affairs are out in the open, the fantasy and escapism is stripped away and suddenly, the affair partners are forced to face reality. It might take a few weeks while the novelty wears off, but so often, men realise with blinding clarity that they have been incredibly stupid and the OW is not so great after all. You hold a lot of cards at the moment - what you do now is going to be so important.
Get help from any source you can, wail and cry and be kind to yourself. The only one I want you to pretend with is him - show him you are getting along without him and can already see the opportunities ahead and it is a much better wake-up call than someone who is devasted like you are.
Finally, don't underestimate the shock you must be in. You will not see his behaviour rationally at the moment and that is to be expected. Give yourself a break and get some great hugs from those closest to you. Don't go for counselling yet - you are still in shock. Do go for counselling later on down the line though.
And keep posting.