There is no device by which to judge a man. Apart from the man himself and his own measures. Who cheated on who? Did she, indeed, cheat on you? Or are you merely internalizing her deeds? If so, then towards what end?
She has cheated. That is the fact. Hasn't she cheated on herself primarily? Whom did she promise first to keep the marriage? Herself or you? If she has cheated herself, primarily then she must answer her own self prior to answering you. And if she has already answered herself then she need not ever answer you.
Somehow, someway, you let yourself go. You let the root point leave you and you must now try to grasp it again. The point being that a marriage is, afterall, an illusion - it isn't reality. Reality still binds you entirely and absolutely only to yourself. You can never live for another being. You can only live for yourself. Fact being, there is in reality nothing such as selflessness. Crude though this maybe, it is ultimately the reason for something like marriage to exist in the first place. And if marriage exists for it then so does separation, as well as longing. You forgot that you were, despite being married, only living for your own-self. You provided to yourself ideals which seemed to be grand for you. Ideals, such as those of responsibility and provided your ownself a purpose based on those ideals. You accepted the responsibility and the purpose but you negated yourself out of the whole picture. You must realize yourself within that picture again. Who you are is not at all linked to why she cheated on you. She cheated only on herself and could not have possibly cheated on you. For she too exists only for herself. The responsibility which you accepted, she was never obliged to also accept. You had wanted that. Every crude law of society expected her to, but in reality there was nothing that could have ever compelled her to do so. Nothing, except her own damned self. And she has left you, for another. You saw his face too. We have both seen his face. You, and absolutely you are entitled to the hatred you feel towards her right now. You are absolutely entitled to that. Yet, you may not mistaken her involvement with another as a cheating on you. You are no where in that picture. Your hatred, hence is also nowhere in that picture. Your hatred is also yours alone, just as your love was.