what actually makes a couple "your" couple... is it just chemistry or something else

been thinking about this a lot lately. we have couples we play with regularly that are fine and fun but theyre not "our" couple if you know what i mean... no real connection beyond the bedroom. then theres this one couple in cork we met 8 months ago who are just our people somehow. trying to figure out what the actual ingredient is. is it that the wives get on as much as the husbands? is it shared life stage? is it that nobody is overly dominant in the dynamic? id love to hear what others think makes that magic combination cos i feel like if i could identify it id be better at filtering meets