Originally Posted by Polywaw
Oddly enough, a simple term might help. Friends-with-benefits. I don't see it used in terms of established relationships and poly very often, but I can see how it fits what you're looking for. It's something my wife and I have dealt with.
A friend you can connect to, hang out, go to movies, play video games, see your kids play together, chat about life, anything everything etc. And yeah, at times, when sex happens, it happens and is a good, non-weird thing.
I don't really like the term "Friends with Benefits" that much, simply because it has come to be used mostly as someone you call just for sex. SourGirl had once suggested the term "Lover-Friend," which I really like.