my partner left me for one of our play partners and i can't breathe

so the thing we were always told wouldn't happen, happened. we played with this couple for like 14 months on and off, became actual friends, double dates the lot. somewhere along the way she and the other bloke caught proper feelings and they hid it for months apparently... i found out cuz the other wife messaged me crying. now my partner of 9 yrs has moved into a flat with him and the other wife and me are texting each other like survivors of the same crash. i feel so stupid... we had the rules, we had the check ins, we did everything "right" and it still blew up. anyone else been on this side of it? how long til the chest stops hurting...