Just chiming in to say, good luck first and foremost. I did this last year and even though I'd lived in England for several years previously before going back to the US, it was still a tough transition and I can relate to a lot of what you're saying:
We're on the opposite side of London, DH got a pay rise coming here, I took a small hit. We share finances and all, but I know it's still hard to not think about what you had in the US. And it's especially hard not to take it personally. Have you considered volunteering work that you'd be interested in doing -- for say six months -- which would give you someone to use as a UK reference and a way to make your CV look more English?
My husband regrets not getting his US citizenship when he could have, but at the same time I remind him of the taxes situation and I think that very slightly eases the blow.
And I definitely get what you mean about expat groups--but I can say having a coffee or playdates with friendly folks from this site does make a difference and it's so easy in London! Good luck.