Such a situation would present a number of complex situations depending on the dynamics within the relationship. However, my personal decision would be to end the relationship and continue down my life’s path without the partner who somehow felt it necessary to cheat on me.
Many people say you should talk and work things out, yet regardless of all the so called fixed relationships once that betrayal of you is enacted you will never forget it. Sure you can push it to the back of your mind but in reality you know that it was an intimate and emotional wound that will always remain. You may come to trust a partner once more after such betrayal but ask yourself honestly in the end will they ever be able to once more gain 100% of your trust and respect. Unfortunately, their betrayal will always pop back into your mind every time something seems a little out of kilter.
I believe that therapy and talking about infidelity after the fact is nothing but a desperate attempt to avoid a major change in one’s life dynamic. If you truly meant so very much to them they would have approached you about their problems or possibly suggested the two of you obtain counseling before they act out in such a manner. Once the horse is out of the stall it does no good to close the gate and pretend the horse is still there. The sad fact is your partner felt they were justified regardless of the specifics in seeking out intimate relations with others. Thus they will continue to believe that they are justified in taking a similar level of action every time they are faced with a comparative hurdle within your relationship.