I remember that thread too.
And I recall correctly, lots of people said then that you were being a walkover.
I can't remember exactly but wasn't there some question about her taking a % of your inheritance too?
Either way, I wouldn't be funding her lifestyle now, and I wouldn't be giving her free access to the joint account. If I were you, I'd continue to pay the bills as required, including the groceries, but I wouldn't be giving her access to spending money so that she can go out and date.
She's being deeply unreasonable and uncaring about your needs. You need to toughen up or else she'll take you for a complete mug.
She's not cheating but flaunting her affair in your face is pretty shitty behaviour. Certainly not the behaviour of two people who have amicably agreed to split.
You make sure everything essential is paid for, and that all your DC's needs are covered, but if she's not going to be considerate towards how you feel, then you don't need to be rolling over and letting her take you for a fool. Get a good solicitor and get legal advice on where you stand - and then you can decide how much you're willing to fight her.