I understand your feelings WhatNext, (been cheated on too - exW in my case) but you come across as very heavily invested in your exH still.
It's understandable to feel betrayed here, but almost all your anger and hurt seems to be directed at him and not her - and she's the one that'll have broken the confidence (if she even has).
I very much doubt she and your ex would have wanted to sit through a date discussing you and your feelings. I can't think of anything less likely to lead to a relationship forming. She doesn't owe you anything - a friend of a friend is hardly a close relationship - and he didn't tell you before the second date because, well, why would (or should) he?
You're both free agents now, although he sounds more "free" of your marriage than you currently are. He'd have been cruel to tell you before the first date - what if they'd met and it had bombed? Why would he have wanted to tell you before they both thought it might go somewhere?
FWIW, if she's only just out of a relationship and is as upset about that as you say, then their relationship is already on rocky ground, but that's really beside the point.
The trouble is that you sound like you also need longer to get over the end of your marriage. If I were your current BF reading your OP then I'd be doing you the favour of calling time on things because I wouldn't think you've moved on.