The counsellor basically told you to live a lie, which is hugely in his interests and massively costs you. It is not in the kids interests to live in this marriage or watch this man do this to their mother. And the longer you stay after finding this out, the more you normalise it and the less likely you are to leave - what matters most to their longterm interests, faking a happy Christmas (HOW? Are you not meant to be human?!) or ensuring them a less toxic future? That is NOT a good counsellor. That's someone whose main goal is to preserve the marriage at all (and in this case all yours) costs.
He's lied to you about asking his parents, and now you know his father taught him it was okay to live this way. Do you want to repeat that lesson for your kids, or do you want to teach them this behaviour has consequences?
He has fucked around, lied to you, and is now using the mental health problems HIS BEHAVIOUR has caused you to bully you.
You need a counsellor OF YOUR OWN and you need a solicitor. You need them before the end of the week, and you need, IMO, to start divorce proceedings against him. That way you CAN get him to leave, because the settlement will force that.
You haven't thrown your marriage away, you didn't do this to your kids. He has, is, and fully intends to. Of course you're angry and devastated, and those reactions are just more of the inevitable consequences of his behaviour.
He does not care how much harm he does you or your children or how much pain he causes. He just wants to have everything as he wants it and fuck anyone else's needs, rights or wishes. And he will do it no matter who he is with, because he feels entitled to do it.
It's emotional abuse. You are living with an abuser. Leave him - please. 