First soft swap, things got real and my body just... shut down. is this a thing

still kinda processing this and i need to know if im alone in it or if its a known phenomenon. m37, dw 35, weve been working up to this for like a year. found a couple we genuinely clicked with, three meets, slow build, all good. last weekend we finally went for it. their place. dim lighting. drinks. some kissing across the room. you know how it goes. soft swap only, agreed beforehand, four times confirmed. so we're a few cocktails in and the other guy is making out with my wife on the sofa and shes clearly into it and his wife is sat next to me with her hand on my thigh and im. fully. soft. like not just nervous-soft. completely body-said-no soft. and the more i tried to mentally push thru the worse it got. she was lovely about it, made a joke, offered to stop, get water, slow down. we ended up just kissing for a bit and then everyone wrapped it up early and pretended it wasnt a thing. drove home in silence. dw asked if i was ok. i wasnt. heres the q. was that my body telling me i actually dont want this? or was that just stage fright that everyone gets first time? bc id been so excited in theory all week and then in the moment my libido straight up nope'd. has this happened to anyone else and did it get better with more exposure, or did it stay that way and you realised the LS isnt for you?