Hi OP
You asked the question:
That sense that anything I say to my H is discounted as it has no value, no credence, no nothing, I am literally invisible to him. And yet he is still so angry with me too. Why? Just why? Is it because I'm not younger, not tall and slim like the OW, don't have her bouncy shining hair but instead a rapidly diminishing mess on my head that Wurzel Gummidge would be proud to sport?
The answer is of course that you are a reminder to him of what a shit he is and how awful his behaviour has been. The anger is there because you are in the way of him doing what he wants and he can see what he has done to you and is in danger of feeling the guilt. So, he tries to offload and deflect the guilt onto you by his anger with you. Please know that you didn't cause this by doing anything. It is all his doing. The guilt is all his. You have nothing to feel guilty for.
Right now, the OW hasn't left her DH for him so he is probably making all kinds of promises to her including a nice big place to live. He can't deliver on these promises until he has thrown you and his own DC out of their existing home. This is a major shitty thing to do so he wants to compartmentalize it along with everything else. Otherwise he might see himself for what he really is and he doesn't intend to do that.
Please cancel any more EA visits and don't do anything further on this yet. You have 3 valuations which is enough for now for any divorce paperwork. If he tries to impose anything else, just say you're unwell and not up to it. Any more EA visits that he sets up, either don't allow them in or answer the door in a dressing gown of doom, holding a tissue to your face (and bucket for extra effect) and tell them you have norovirus. That should get rid of them for a few weeks.
Yes, you may eventually have to sell, but you can stall the process as long as possible. He will be cross as this won't be what he wants and the longer he delays delivering on his promises to the OW, the less likely she will be to leave her DH for him. If she doesn't leave her DH, he will have blown up his marriage and nice comfortable life for nothing. I hope when this day comes you will have realised how toxic he is and automatically protect yourself by refusing to have him back. He is not the person you knew. This new person is really nasty. You loved the old him, not the one that is now there.
Please for your sake, try to avoid spending any time with him as it is too toxic for you. If he needs to come round, he has to make an appointment and you will be out and your DB or someone else there instead. They will keep an eye on him so he doesn't take anything he shouldn't.