Sorry this happened. What inspired him to suddenly make this urgent confession?
While he asked you to keep it private, you're not his therapist so he can't expect confidentiality. He's responsible for what leaves his mouth..
It's not your job to second guess his therapist and he shouldn't have asked you.
Please stay out of his business and don't get involved with with mental health issues therapists and marital problems.
He seems to be looking for drama putting people in ridiculous situations. Let the dust settle.