For fucks sake, do not believe that he won't be doing this again, as soon as things calm down at home. It is what gets his rocks off. You can't compete with this. You are the wifey at home, who he has had sex with for years (in his eyes boring), whereas what really floats his boat, is illicit sex with prostitutes that are young enough to be his children. Fancy trying to compete with that, for the next 20 years? I don't fucking think so.
He is still lying to you : no above board salon would offer to wank off a client, ffs. If your husband had been offended, he could have gotten her the sack. So, that's a fucking lie.
This isn't a drunken snog at the Christmas party, where he has woken up and been filled with guilt and remorse. This is multiple occasions of him soberly seeking out sex workers, whilst behaving so normally around you, that you had absolutely no suspicion.
The 12 you've found will not be the whole story. No chance. And if he can seek out this paid for sex, you can bet your house that he shags anything that moves whilst away on business/Christmas office party/lads nights out, when he meets women who are up for a bit of sex, and it's free.
You won't change him. He needs this. It's who he is. He will just get better at hiding it. And even if you could change him, and stop this shagging around, do you want a man that is faithful, just because he's on a tight reign, rather than a man who is faithful because he adores the bones of you?
Even is he doesn't cheat again, he will always want sex with other women, he needs it enough to pay for it. He wants it so much, he is willing to risk his whole life as he knows it, to get it. Imagine how strong that desire must be....and think about what a tight grip on him you'll have to have, in order to stop him seeking it out again. Can you be fucking bothered?
I had to re-read Godmothers posts, as her situation was the exact same as mine. 20 years. Continual cheating. He just couldn't stop. I left and now have a lovely DH who is very different. ExH cheated on every woman after me. He now has a serious GF of 4 years and they're moving in together...guess what, he's cheating on her.
I say dump him. Let him shag around until his little cock is on fire. You meanwhile, can rebuild, and in time meet a nice man who doesn't pay women young enough to be his daughter, to jizz in her hands.