What did he do wrong? Well for starters, he claims to be a "therapist", while continually seeking a dopamine hit hourly by posting 30x a day.
Then, he decided to air his buddy out online under the guise of "Ts and Ps", without giving details. He claims they have "an incredibly close friendship".
When the sht hits the fan, because all of these people post way too much on the internet, Therapist claims he didn't know of the allegations of his "incredibly close friend". (Which seems hard to believe, given that TA found it in 10 mins).
So, he never should have taken it to the internet. If he was a therapist, he should have also advised his buddy not to take it to the internet himself. Then, he continued responding after the whole thing blew up, quite defensively, which a "therapist" would have known it was immediately time to walk away from after the OP.
A therapist also should have advised his buddy that it's not a good idea for a woman he's known less than a year and had 3 kids to be marrying him as he's headed off to jail for a good long while, for doing something to his ex-wife while his own kid was present.
But then again, this person is not a therapist, but holds him out as such online (when he should know better if he were) and continues posting every waking thought online.
So he either wanted a soap opera about some guy he knew since multiple people here knew the guy and gal (possible given his need for internet blue star dopamine), was too stupid to realize that taking it to the internet would cause a shtshow (likely if any of the personal detail he's put on the internet is actually true), or is so unselfaware of anything (likely if he is actually in the therapy field and is still posting in the manner he does online). Or some combination of all of those.