I wouldn't never have that problem, because I don't believe in implicit relationship contracts denoting "only me". She could do whatever she wanted. I would do whatever I wanted. We would simply live life namely together. We would do what made us happy. If it made her more content or happy to go out and get some extra loving, I would not condemn her for it. I would not set the basis of our relationship on her never doing an implicit list of things. "I will love you forever, unless you cheat on me, forget to put the dishes up, don't walk the dogs, insult my sister, spend too much time with your friends, don't pay me enough attention," etc. etc. The list goes on and on.
Adam is a man she used to fuck, and he knows it. Zoe Barnes is a woman he was currently sleeping with, and she knows it. Their love runs deeper than mistakes or sexuality.
In my opinion, if a person cannot forgive someone for a mistake, then they have no business getting married and saying "till death do us part" or no business saying they're in love. If you don't really love that person, then hey. No point in sticking around. But, to me, real love is something that doesn't give a shit about anything else but being with the one you love. It isn't contingent on a set of behaviors. Perhaps that's idealistic. But that's what I believe.