This is a really helpful thread to me and I am enjoying reading everyone's responses. Since coming here, I have been thinking about these labels and where I fit in.
We opened up our relationship for casual sex with other partners. No real rules except to use condoms. Husband is content with a very occasional one-night stand, but I quickly began having the casual sex with one specific piece on the side.
The arrangement with that man is still ongoing, and we have developed affection and what is, I hope, a good friendship (and not based purely on the sex). But, really, all we are to each other right now is casual sex partners. There's no saying casual sex can't be friendly. He's not, you know, my boyfriend or anything.
So I think I'm still in an open, non-poly marriage. But who knows? Maybe I should say I'm poly-ish.