1. What is the key/core relationship here? Couples are rarely "balanced" (All are equally fiends with each other, and all met at the same time), usually the women, or the men are the core friends, and the spouses are incidental..(this becomes apparent in divorces, as to which party gets to keep which friends)

2. I am guessing it may be the women, in which case, it now revert to just the girls, and not as couples. Under no circumstances have an event where the offending guy is part of the picture (this probably drops contact down severely)
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OR
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3. The other couple are not long for this world -  as a couple. Solution? - stay away from both, until the dust settles...