I think it's important for an LBS in an infidelity situation to truly grok the "I'm already dead" principle.
I think that in Zig and Brit's sitches, they have that understanding.
So there's no M to save. Now... it's just a matter of doing what ever works for them.
To put it in vulgar terms, their H's are just another piece of meat.
I don't see either as being desperate and setting themselves up to be abused. I also see them both struggling with the idea of seducing an attached man. And I see that as positives, in them.
Yet, if they do what they do... really embrace their feminine side... and their Hs are simple creatures... it MAY draw their Hs back to them. That would then be an appropriate time for them to set boundaries with their H's. "IF you want some of dis... then u gotta ditch bimbo..."