I was lucky enough back in the '90's to be in several MMF's where the husband was bi like myself. Two of these were long term relationships, a year or two for both. We never discussed any real dynamics between us, and that may have been the point of failure, bring either of these to an end. I have to admit, at that point in my life I was a bit clueless about relationship protocols, imagine Sheldon Cooper-ish (guy on the Big Bang Theory TV show) thought processes but not to that extreme. I never tried to be the wife's lover and only had sex with the wives when we were all together, however the husbands and I had sex on our at times. Great times while they lasted.