Originally Posted by serialmonogamist
When you're a single person hanging out with someone else's (monogamous) partner, they are likely feeling concerned if you start spending a lot of time as friends together. It is also likely that when you're not around, your friend's partner is going to be asking a lot of questions about why you're such good friends and where it's leading. Even if you promise that it's just friendship, there's likely to be some insecurity and jealousy. So making it explicitly "platonic polyamory" would hopefully resolve the tension of monogamous expectations and fears. Especially if the couple you were dealing with already had an open relationship, it would be that much less problem for you to develop a strong friendship, don't you think?
Not at all. I have a very good female friend with which I spend a lot of time, and I don't think it is a supposition to say that TP has ever been jealous, and I have brought up with this friend how her fiancée feels about our friendship and have asked him directly; both answers (to preclude him placating me to escape an awkward question) were the same, he's not jealous and never has been.
Your example assumes that jealousy and suspicion are certain as a result of a platonic (and I'm using the commonly accepted definition, not your contextual one) relationship.