It is that your whole world ended. The pain is the same as if someone you loved, died in your arms.
You don’t want to believe it; there must be another explanation. And the more you trusted, the more it hurts.There is separation, there is divorce, and all the confusion and pain that causes.
There is also the wiser step of maintaining a form of the relationship until such time you are thinking clearly. For Adultery can and does cause a kind of madness; in which people have committed murder.
What you need to do if you can, is pause until you have redeveloped your life to the extent that a separation or divorce will not be particularly disruptive.
You need time to process, to heal, time to decide from a position of strength, not weakness.When you are the one betrayed you may act insane, make idiotic decisions, lose control.
This is why I advise that you pause. Pause and try to put yourself back together before you make a decision.