Summarize:

Reach out to a third party to get their take about how you should move forward. Explain exactly what happened to the person and ask for their feedback.  Choose someone who you can trust to keep your secret. Someone who is older and/or wiser often makes a great advisor. For example, if you have a coworker or friend who healed their relationship after cheating, they might be a good choice to confide in. Avoid confiding in someone who might feel guilty about keeping your secret or who might be overly judgmental about you hurting your partner. Go to the person and say, "I made a huge mistake and cheated. I know it was wrong, but I don't want it to ruin my relationship." Then, go on to explain the events leading up to the cheating and ask for specific advice, like whether you should break the news to your partner and how to do that. Look for support groups in your city or online that cater to people who have cheated. Here, you can talk to others who have dealt with guilt and find out how they overcame it. Guilt often intensifies when you put up walls and isolate from others. By opening up to people who can relate to your situation, you can work to overcome guilt. If you have spiritual or religious beliefs, try consulting with an advisor you respect. A spiritual leader will be able to listen to you without casting judgment and offer you practical solutions for overcoming the guilt you feel. Ask your spiritual advisor for an in-person meeting in which you can seek support and guidance about the dilemma. This person may be able to offer you valuable counseling on your own and with your partner, if it comes to that.
Get the advice of someone you trust. Participate in an online or local support group. Seek spiritual advice.