I think maybe the debate here over the word addiction is because it carries the implication that it's not his fault. When we talk about addiction usually, it's with the knowledge that the person has a physical dependency and needs understanding and support to break it. Self-discipline isn't enough to break an addiction.
I think the situation with your husband is very different OP, and that's perhaps why the use of the word addiction is rankling. if it's helping you, then it doesn't matter what you want to call it, but it perhaps has different connotations to us looking in from the outside.
FWIW, I am autistic and have ADHD and tend to develop overwhelming fixations on things. When I'm in the moment, it's all-encompassing and I really am not very interested in anything else, truth be told. However, as a responsible adult, that's not actually possible because I have to work and look after the DC, etc. I understand what obsession feels like but I don't think it absolves you of any responsibility to make the right choices. It's perfectly possible - he just doesn't want to and doesn't see why he should. And that's the issue.
I do wonder if a PP nailed it with the suggestion that he genuinely doesn't believe he's done anything wrong. If he really does just see it as a close friendship and doesn't harbour romantic feelings, he may be spectacularly missing the point of why you're upset.
I'm glad the counsellor was clear about his behaviour not being acceptable. Thank you for taking the time to update here, it must be really horrible for you right now. You sound really strong, so if nothing else positive comes from this, there is that 💐