OP, you have to start thinking about this in a different way (and quickly). You need to start thinking of your wife as a vulnerable adult and you are the only one who is going to advocate and fight for her.
It sounds like your wife is in an abusive relationship with her counsellor. Alienating the victim from family and friends is classic abuser territory. The level of dependency she has on him is highly worrying and very unprofessional. Normal counsellors do not operate in the way he is (listen to the pps who have experienced abuse and what sort of therapy they received. A pp mentioned how can he possibly see your wife as much as he does. What about his other patients? Why can he see her regularly at short notice? He obviously doesn’t keep normal hours and if these are “emergency” sessions, the level of contact would suggest that so thing substantive needs to happen rather than just meeting in car parks).
Have you researched how csa effects adults? From what you’ve written, she experienced severe abuse for 18 years (what was the frequency? Daily? Weekly?). That level of abuse would have consequences. People who have been abused react to the world/people in certain ways and with recognisable characteristics (attachment issues, anger, violence, constantly seeking approval etc). Before the allegations were raised, what was your wife like? How did she interact with her family? Was there anything that made you think there was something “off”?
Have you seen the photographs of the birthday parties? Do you think she had birthday parties? Who said the photos were altered? If it came from him that shows you he is manipulating his wife rather than helping her.
Who gave your wife this man’s name? Can you contact to find out what they think of him? Don’t mention details, but ask some questions.
Jut because someone is a therapist, doesn’t mean they are a good person. He has made a lot of money from your wife and he may be one of these awful people who like being in a position of power with a vulnerable person. They get off on being needed and being looked up to. If he feeds of your wife’s need, he is going to have answers for everything. Couple sessions...not in her interest. Police involvement...not in her interest. There will be nothing that’s “in her interest” other than keeping her dependent on him.
The professional body said “normally”. That does not mean never. Have you asked them what there guidance is on revelations of abuse? If not, do so.
You need to look into counsellor/patient dependent relationships. Yes therapy can take years, but have you seen an improvement in the time your wife has been seeing this man? A real improvement?
Have you been in contact with her family? Do they know what is going on or why they have been dropped by your wife? There is a possibility that the abuse occurred, but with what you’ve said there would be corroboration somewhere. Was your wife the only one abused? Out of hundreds of people, no-one has ever mentioned this? No investigations? No other allegations?
This man is stealing your wife’s life. If she was abused, she needs treatment that works. If she wasn’t, he has broken her relationship with you and taken away her family relationships. That is not right.
How does she interact with your children and how old are they? They’re are also being effected by this and their relationship with her will suffer if this is allowed to continue. If everything is above board then John will happily answer some questions. If it’s not, he will block questions and not offer any answers.
Please start doing all you can to find out how to help your wife.