If this man's own father lives with you, then surely it ought to be more important that nothing happens to rock the boat at home?
How bloody DARE he pile on the responsibility of this affair of HIS onto your shoulders. If I leave what about my poor father, if I leave what about the DC... Erm why didn't HE think about that in the THREE YEARS he was cozying up to this thoroughly poisonous individual?
He wrecked it all, he had it all in the palm of his hand and for the sake of a fling with a woman who clearly has no respect for herself let alone a supposed friends's marriage.
He deserves NOTHING, not a thing, only a hobnailed boot up his arse and his possessions scattered about the pavement.
No affair is a good affair, but the one that is between a woman's H and her Friend is particularly cruel, utter betrayal by TWO trusted people, AND the ripping of a vital support network from your life.
I know that there are people connected to this OW and you, but make sure they know what she has said and done, and remind people that you never, ever want to hear about her because of it.
Repeat the same about your H too. The laundry is only dirty because THEY made it so.
He is only insisting on you going to counselling because he knows you won't go... Why?, because the way you are feeling is right, you HAVE been let down, there is no way to help you feel better about what this man has done to you because he is STILL not taking full responsibility for it.
If he were, he'd not be talking of HATE of the OW. He HATES the fact it all came out into the open, that's what he HATES.
You have to put YOU first, ONLY when you are happy, contented, relaxed and confident can you provide the very best environment for your DC to grow and develop. By sticking this out, you are somehow teaching them that what your H and his OW did to you is OK, and nothing really important. Sticking with this is devaluing you every day, to yourself and to your DC.
You are worth more than this, draw up all the strength you need from wherever you need it and ROAR. Demand your space, your rights and his departure.