I'm poly, and my partner's mono.
It seems that what bothers you most is the NRE shining in your face when your partner's OL is visiting. Is it possible for her weekend trysts to happen at his place? At a hotel? For you to be somewhere else when he's around?
And yes, the holy grail is to find another couple with whom you have mutual exchange attraction, but those, as you mention, are long shots. While you continue to search (if you're partner would want to add another love), you both might want to continue in periodic swinging adventures.