yes there are lots of options you can use a tinder or local hookup app and couples create profiles on certain apps where swipers know that they are looking for threesomes

however i also do note it shows much mental maturity for you to take your partner into consideration as much as you did and you noted their level of ok with the whole situation and just because it doesn't work out with him doesn't mean that it can't work out with another person and you guys can use the time and explore options together and use it as a hot and different way to keep the romance going a random reward every six months or once a year in the form of a threesome sounds pretty dope to any guy but that your girl is into just shows you guys are at a great place relationship wise because you're open with discussions and listening to the others evolving needs. so right there you're a few steps ahead of other couples who keep going for yearsssss and just fall into the routine

just be sure to get the other person tested if you don't know their sexual history in 2017 no one can stress that enough