when I was in therapy the option for my wife to attend as well was always there, but neither of us felt it was right for us, and we did discuss it a lot.
For me it was the feeling that having her witness my descritions of my abuse would in someway cause her to 'assume' some of the guilt and shame that I was trying so hard to escape.
To this day I have never told her details of my abuse, or my acting out as an adult. She know's what happened, as in what kind of sex acts went on, but not in as much detail that I shared with my therapist. Neither of us thought that she would benefit herself, or understand my situation any better if she knew the details.
Since then I've begun to work for the charity that provided my therapy and done most of the training to become a counsellor, and although I'm no expert I read and research a lot.
A good therapist will (usually) lead, not ask, the client. They provide the safe environment where the client can, when they're ready, disclose and deal with anything that comes up. So the 'deep stuff' can come up anytime the client feels safe and confident.
Personally I would try to avoid that happening when the clients partner was with them, for the client it presents another level of concern - "what will my partner think if I say xxxxxx?" and that can lead to them changing their minds and not disclosing fully ( at that time maybe ? )
If they are alone with the therapist then they should ( hopefully ) feel able to disclose virtually anything without fear of judgement, and that's a good place to test the waters.
I disclosed more ( but not the full sordid details ) to my wife after I'd tested my thoughts in therapy. That way I felt I could offer the complete, or at least a better, explanation to my wife, which I generally did.
I'm not saying don't continue as you are, or that the therapist is wrong, they all work in their own ways.
All I'm offering is another view.
Go confidently in the direction of your dreams! Live the life you've imagined. As you simplify your life, the laws of the universe will be simpler.
Henry David Thoreau