Your couple sounds, to me, like they were just swinging. I could be way off here. If you are able to, maybe go to dinner with them or bbq, but do it just as friends.
When K and I first started swinging, we were "exclusive" with them and them with us. But it kinda went sour after the woman in the other couple developed feelings for me. She didn't understand and didn't know how to handle them, so she cut everything off, it hurt. K and I are still very close with the male in the couple and they have since divorced, making the whole situation easier on all of us. All of us were very young and it was only suppose to be for fun, but when you interact with someone that many times in that way there are bound to be some emotions mixed in with it.
Hey I just realized something, I had strong feelings for this woman(love?). Maybe I'm not quite as mono as I thought.
I would rather be hurt by your honest than pleasured by you lies!