I think I can see where you're at Lucy, but this too will pass.
This OW is a renewed threat now that her H has chucked her out. I suspect you fear that if you do the same, your H might go to her. You want her to be in misery and to have a double punishment (loss of her H and her OM) and as long as you say you will try to forgive, you can keep him there with you and away from her. If you do feel like this, it's entirely normal and understandable, but it isn't the end story.
It's also entirely normal at this stage to view her as predatory - and to take comfort in the realisation that she is no goddess and that you are better than her in every way.
At the moment, you are in "fight" mode and that involves a very strong, primal competitive instinct. Posters who have been in this situation will recognise it and empathise, others who haven't will not - and will tell you that he is not a prize worth fighting for and that the women involved should not be "fighting" over him.
You will come out of this phase and eventually you will conclude that both of them were equally culpable. You will also one day conclude that this had nothing to do with you whatsoever. It wouldn't have mattered if you were 100 times more attractive or successful than the OW, or if you had been administering to his every whim. This isn't about you, it's about him. His ability to turn down a certainty, his ability to deceive and lie, the choices he had and the decisions he made.
You have absolutely no culpability for this affair. You only had a responsibility to your marriage.
He might be as outwardly remorseful as it's possible to be, but the fact that he has tried to shift blame - to you and the OW - is telling.
Counselling is good, but please go separately.
The physical pain you feel is real and many of us will recognise it.
You will only start to recover when your H starts to take full responsibility and resolves to get to the bottom of his behaviour himself.