This.
His attending councelling is a classic manipulation tactic to support his excuse.
He wants to use this as a means to get you to co operate during his exit, that this 3rd person will calm you and shame you into accepting "people just move on". I wouldn't waste money on it, seek solo councelling.
You said the councellor said he was just a pasenger in your relationship, maybe he wants to get on another bus. Maybe his "passenger' personality has made him meet someone just as forthright and capable as you, and she wants action, the action of him leaving his family for her.
Who knows he could be bullshitting the councellor pretending to be passive, when in fact he's actually a full on narc, with the capability of having a double life.
Op you do not have any of the facts, you are relating and trying to trust a man that may not exist, really protect yourself, ducks in a row in case, be mindful of the finances, he could be ready to bolt.
I really hope this is not the case but you are currently bewildered, you are at the 'ask the audience stage' after the coucelling has not brought up any answers, you need to investigate, instead of the 'phone a friend" next stage look through his phone.
I honestly don't think depressed people are that organised, to go to joint councelling, preparing for an actual split, it all sounds too controlled on his behalf.
All this looks like is a tick box exercise in pulling the wool over your eyes and him attaining victim status.