This happened to us.
We discovered early on that a male friend of my wife's was attracted to her and vise versa. I asked her to explore the avenue to see where it could go. The one thing about it was the male friend was married and for the life of me i could not read the woman. We knew his thoughts but could not get a guage on her at all. Well we set some ground rules that the wife could continue in order to find out more *but* she wasn't to do anything without me there. She ended up having the guy over one afternoon after work and kissing him. Well to say the least i was severly pissed since swinging is a mutal thing. PLUS there is no way i wanted any part of breaking up a marriage in any way.
You have to be both on the same page. Yes there will be growing pains and there are other's here that are a hell of a lot more experienced than us but without being on the same page it won't work. Suffice to say that in the end we did end up connecting with the man and wife and it's early on, just happened, but it looks fantastic for the future.
Put it this way, some are lucky but we have not been. We started out nearly 10 years ago looking to swing and up until a few month's ago found out couple. The attraction goes both ways and i'm extremely lucky that it's worked out this way.
Communication is key, without it it cannot work.
Good luck.
