I wonder if the feelings for Ruby are just a way to get back at Margret...
You can patch it if you really want to.
Unfortunately Margret seems opposed to MY fantasy of a big poly amorous relationship...
Tho she DID cheat so maybe she's just in denial about that part of herself.
I think you should both agree in the future to let the other person know if you have feelings for someone else while you are together before acting it out like Margret did.
And I also think Margret owes you 1 "cheat" pass if she wants to get back together (using it is up to you).
Cheers