I've cheated, now what do I do?

Cheating is one of the most serious ways to damage any relationship. Relationships are based on honesty and trust, and you've just sliced open both of them. You need to start rebuilding right now, and that begins with being honest and taking the consequences of your action. Lying or hiding it is unfair to your partner for many reasons. What if they hear about it from somewhere else? They deserve to know the truth, and you are failing in your responsibility if you lie to them in order to shield yourself from the consequences of what you chose to do.

So talk about it, face to face, somewhere quiet and private. Explain what you did, and why you did it, and apologize for the pain you caused. Let your partner vent. They have been betrayed and have every right to be angry and upset. Realize that the healing process will take a while, but that it can actually start to happen now that everything has been worked on. What you had before was a festering boil that would only get worse over time. Now that it's lanced, the process is painful, but many relationships heal to become even stronger than before.