if you are 99.9% certain hes done it theres clearly no trust and that alone is potentially enough to leave him.
on the other hand i dont necessarily agree with many of the posters on this thread.
one referred to the prostitute as a 'whore' which didnt sit well for me. theres no need to demean the sex worker, shes done nothing wrong, its her way of earning money. if your oh has cheated hes in the wrong not her.
Secondly, i also disagree with it being 'rape'. if he has, he isnt a rapist. i know for a fact some women enjoy their job as sex workers. im not saying all do, or there arent women who are forced into it, all im saying is dont hate her.
i am a firm believer curiosity is a wonderful thing most of the time. my dh is honest that he watches porn, and honestly so do i. we watch it separately and together. sometomes i google various sexual things as im curious. i imagine he does too.
he hasnt necessarily cheated, he may be feeling pushed out and curious. dont jump the gun. he may not have acted on his curiosity.
the people saying he would have looked at pron instead- it might be the idea of an escort that excites him rather than porn. it may be a little fantasy (hurtful though it is) that he hasnt acted on, is simply... getting off on (sorry for crudeness of that phrase!)
leave it, mull it over and talk to him. dont take shit. youll know if hes lying if youve been together for so long.
i hope everything works out. 