I believe it is always best to speak the truth even if it is not easy or comfortable to do so. But it is your decision, of course.

I think he ought to hear the truth, your truth. Why? First, because it *is* how you truly feel and this voice needs to be heard or at least expressed. Secondly, it might help him realise how he is with clients and how potentially damaging it is to be biased or dismissive of one partner.

At the end of the day, he was not good enough for you and he let you down majorly. You don't need to go 'all guns blazing' but I think (again, your decision) he needs to hear how this 'relationship' wasn't working for you.