Dd also wants to live with both of us and has really developed a great relationship with him after not really liking him before.
Just so am understanding right - DH is not DD's father?
How old is DD?
Where I'm going is - actually whether he's her father or not - a child can't really tell if someone is good or not like that, and can't decide, I think. Clearly you love DH very much and want it to work out. It's so good you've been to therapy and have sorted a lot out, and got a nice place to live. Your therapist should, actually, have told you at the first meeting that if you said anything she felt might mean a child was in danger, or that you were in danger or might hurt someone else, then she'd have to report it or risk losing her licence.
If you want complete control over your life, and there are difficult things in it, then you actually can't confide in those things to a therapist. The problem is that although there are some very clear cases where harm is a risk, there are a lot of others where the therapist will know some but not all details, and will try to get a picture, and will have to err on the side of caution, because any risk is unacceptable. IE, there might not be a real reason to be worried, but they have to play safe.
To be honest, I think her concern here is that you are swayed by your DH - you love him and you would put up with a lot, and your DD is in your care, so she is also part of this. To leave her alone with him when he is unwakeable is, as I guess you know, not safe for her. I don't know how old she is, but I guess not 12 or so.
Your therapist isn't worried that he'll hurt her. She's worried that you will, eg, let your daughter be in a situation where she could hurt herself by not being properly looked after (you are out, he's off his head).
Two spliffs a night isn't nothing, but a lot of people do it and SS don't know and aren't involved.
I know a woman who takes coke and fucks other people's husbands and has her daughters at private school and seems like a perfect angel - but that's another story. She wouldn't end up with SS at her door in any situation.
I'm afraid you have to understand that now you've spoken about it, even if you stop seeing her, she'll have to raise her concerns.
Personally I think you should take it gently with the moving in. See how he goes. And you probably do have to lie to the therapist if you don't want SS involved. But you also have to put your daughter's wellbeing absolutely first. That's really what this comes down to.
I'm not trying to preach at all. Sorry if it sounds like that : ( A warm relationship with someone good, for you and your daughter, is so important. I hope it works out. Sounds like he's getting it.