Developing friendships as adults is probably one of the most difficult things that anyone encounters. We all want to do it but at the same time we all have a difficult time doing. As was said earlier in the thread, I do think that within a very short amount of time we know whether or not the person we are talking to is someone that we COULD be friends with. And every once in a while you meet that person who is just your BFF from minute one. But once we grew up and got married it got a lot harder. Now short of the instant BFF thing happening, it takes alot more to develop a friendship, for starters there are more people involved. Not only do I have to get along with this person, but my husband does too, and not only does she have to get along with me but her husband does too. We often talk about the 4 way connection required just for two couples to feel comfortable swinging together, but if you want to actually develop a friendship then it requires an even deeper connection. Then take that a step further and include the fact that we're grownups and married and often have kids that take our time and that severely limits our time to really establish a friendship. And for many swinging couples they get so little time where they can go out and do things without the kids that they would prefer to take that limited time and go to a club/ house party/ social or hookup one on one, because that's the only chance they get to do those things.
We are like you, we'd love to meet some couples we could do all the other stuff with, but the reality is, we have a hard time getting our vanilla friends to find enough time to do those things.
So I guess all in all it boils down to, it's hard to make true friends as adults.