A Fish Called Wanda/WMG

Archie was lying about why he broke up with Wanda.
Wanda poses an idle query about how much money he has. He says "not much" -- and then dumps her for her own good. That doesn't make much sense.

But the last time they were together, Archie was found naked in an old acquaintance's house with a woman half his age, which must have been embarrassing. Wouldn't that make a respectable, self-conscious English barrister rethink the relationship?

He only returned to her after his reputation was truly destroyed.

Archie secretly commissioned George and his gang to commit the robbery, intending to grass them out and keep the proceeds himself to finance an escape from his wife.
Seriously, go back and look at the movie. Could any of that happen without it being planned in detail?

His getting Wanda in the end was a "bonus." Or was it....?