Dagferi, someone unearthed a thread from a year ago with you talking about this same challenge so can only imagine how long you've been hurting
Could you please remind us why Butch won't get the BDSM needs/wants met elsewhere? Think you said once because he's so loyal or mono or something but he's loosing his marriage!
Like you said he deserves to have those needs met.
Maybe he doesn't know how to go about exploring those needs outside marriage? Maybe he's afraid of a big or love connection with someone who can fulfill those needs which he feels might jeopardize the marriage? Or???
There's a podcast "polyamory weekly" by Cunning Mix who talks about using a 'pro' as being a way to safely meet needs like that (if you've got the extra cash). Less likely to make attachments that way.
Or in Seattle there's a place called the Center for Sex Positive Culture with tons of events every month catering to different kink/BDSM proclivities. It somehow managed to take all the usual urban underground kink societies and get them all together in one place. Perhaps he can contact them to see if they have any leads in PA and/or explore some of those underground communities that most urban areas have (and several rural as well, I'd imagine).
There are so many options & with the net 'findable' options. Maybe a counselor or the realization that he's going to lose his marriage if he doesn't explore some other options may help him finally hear and understand that you can't fulfill those needs/wants?