Interesting question and look forward to reading more replies
Unfortunately, not much advice we can offer since we're most definitely in that inbetween area as well. I was sorta wondering though if you can just have a relationship with another couple where you're just like fuck-buddies? Like when you're younger and single and you've got a friend of the opposite sex that you just managed to cross just the right lines with. It's probably tougher with singles since someone is always looking for a mate but if you've got a friend that rates somewhere between maybe casual to good friend and you can just have totally no-strings sex with whenever you're both feeling in the mood it doesn't seem like it would be that big a deal if sometimes a little real-life drama sometimes got in the way and one or both of you weren't in the mood. Seems like the same could work for couples. We've got a vanilla couple we're great friends with that we'd never have sex with but we do get extremely sexually flirty with whenever we're all partying together. Honestly, sometimes they're a pain in the ass, totally drive me nuts. But next time we're together we're good again, maybe flirty again. Couldn't that work but just sub sex for flirty?
EDIT: and sorry if I'm side-tracking or confusing things too much...it all made more sense in my head!