I have been trying to be upbeat and pleasant, do nice things for him and not ask too many questions about why he is late etc. I thought things were going pretty well..
Well, of COURSE they were going well -- he's got TWO women "doing nice things for him," he's cake-eating, and not even getting questioned about it from his wife!
I thought you had vowed to change that, after reading DB?
No, we are not to be jerks to our wayward spouses, but we're not to enable them, either. Treat him civilly, and do nice things for YOU ("GAL"), while establishing (and enforcing) some boundaries.
