Married 15 yrs, never even kissed anyone else since the wedding. talk me through your jump

genuinely dont know if im writing this for advice or just to type the words out somewhere safe. m45, dw 43. 15 yrs married, 18 together. ive not so much as kissed another woman since our wedding. she's the only person ive been with physically the entire time. and honestly i was completely fine with that. not in a "settling" way, in a "we built this and im grateful" way. then six months ago she brought up the LS. i thought it was a phase, the conversation paused, came back, paused, came back, and now we've started actually looking at sites. she's been the more enthusiastic one but tbh once i sat with the idea i found it intriguing too. its not the sex with strangers that fascinates me actually, its the idea that ive been living one version of monogamy without ever even seeing what was on the other side of the wall. but. and heres the thing. when i think about ACTUALLY doing something with another person physically, even just a kiss, my brain short circuits. its not moral panic, its not jealousy of her doing the same, its just... 15 yrs of muscle memory says "no, that's not us". i dont know how to override that. people who jumped after a long stretch of pure monogamy — how did you actually take that first step? did you ease in (kissing parties, lifestyle holiday)? did you just rip the band aid? did the muscle memory ever come back to bite you afterwards? did your wife find it easier than you? just wanna hear from people who've been here.