How long have you and fob been broken up? You say his new woman has been with him for about a year, so I'm wondering, why are you still playing at being a family 3 days a week? Like how exactly does that work?
I guess your kids are still fairly young and I appreciate you want what's best for them but I don't see how you and fob pretending to be a family is a good thing. Isn't it confusing for them?
I don't agree with the gf playing mummy to your kids yet at the same time, if she's with the fob, she will be involved. The same will go for a guy that you get serious about.
Speaking from a bit of experience, I have to say that it would be my personal choice to take my kids out separately from him, whether he has a gf or not. I think birthdays and other celebrations should be separate too. You are not a couple anymore so why are you doing couple things? As the product of divorced parents myself, we do two of everything. We celebrate with both sides.
Anyway, that's just my 2 cents so take it for what's it worth. I read all the other replies and while it's nice to have everyone agree with you, to help you feel that you're right, it's not always realistic.
The other option, that works well for lots of people is to trade off and switch every year. That might be something to consider.
ps. smoking is not cool!! I agree with you there!!!