Well, I thought of suggesting that you watch Gaslight, but since you already realized, on your own, that that is what has been going on, your eyes are already open.

On top of this forum is a subforum about Divorce. I would post there. The title should be something along the lines of "An American expat in England is a victim of gaslighting abuse & needs help divorcing his English spouse."

Hopefully this would yield practical advice.