The reason I could post so confidently is that you could have been describing my father & mother 20+ yrs ago. He too found himself another woman, an American. He spun my mother some wonderful lies in order to have the affair; he was just so amazingly self-absorbed - I was quite astonished that such a selfish man lived inside my father - does that resonate in any way?
My mother, like you, was amazingly tolerant, so desperate was she to keep the marriage together for us and for her - she still loved him you see, despite what he had done. Convinced she was could get it back on track being, I suppose, the backbone of the marriage, but of course it takes two.
My father announced one day he had decided - he was going to commit to the OW so my mother filed for divorce. It was almost a cruel spectator sport, watching my father confront his own very disappointed father and the rest of the family (my mother had shielded him up until then).
In the end the OW went back to her much wealthier hb, and my father, much diminished, returned home - only to find my mother didn't want him.
The point I'm eventually getting round to making is that you appear from your posts strong and resourceful. Your hb sounds quite a weak man and will probably go on making, what seems to you and to us, stupid, dick-led and hurtful decisions re this woman - he's certainly not reached a "god, I've been such a twat" nadir that currently would makes your relationship seem salvageable.
Personally, I'd let him find out how costly it is to support two homes - money troubles does rather take the gloss off - expose him to family censure and file for divorce. He might wake up to himself; he might continue to be a twat but gently, but with a firm push, can I suggest it's about time you took charge and protect you and yours?