Hi, I'd like to help you with your question.
There is nothing wrong with the guilt you feel. It is actually a healthy sign. Although too much guilt is hurtful, your guilt is very appropriate.
Guilt serves to tell us that we have done something that goes against a moral code of conduct. It is a healthy emotion that keeps us out of trouble or helps us correct a mistake. It helps us grow and mature. Think about the lessons you have learned by making mistakes. They stay with you and help you not do the same behaviors again, which protects you from getting into trouble.
Accepting that you did something wrong is a good first step in dealing with your guilt. It sounds like this is something you have already done, which is good. You can also make amends, as much as possible. Since your mistake was with someone you might never see again, then it does not make since to go that route. But finding another way to make amends may be possible. If you attend church, you could talk with your pastor about how you feel. Or you could tell your father, if you feel he is supportive. A close friend may also be an option. Living with this mistake alone is making you feel worse. Making amends by sharing what you did and getting support will help break the cycle of guilt.
If you do not have someone to share with, then try writing a letter about your guilt. Apologize for what you did. It does not have to be to anyone in particular, but putting your feelings on paper and saying you are sorry will help.
Learn from your mistake. You are feeling guilty and upset by what you did. That means you learned from what happened. Your choice may not have been a good one for you, but it also taught you that this is something you will not do again. The lesson is staying with you, most likely for life. Considering that some people would make the mistake again and again, you are doing very well.
Realize that no one is perfect. Everyone makes mistakes, no exception. And anyone who learns from their mistakes and grows from them feels guilt and shame which is a healthy response. But accepting that you are not perfect and that you never will be helps. This will not be your last mistake. Accepting that helps you overcome your guilt.
If you feel that you cannot cope and your guilt starts to interfere with your ability to function on a daily basis, consider talking to a therapist. Therapy can help you face your guilt and why is is bothering you. It may be that there is something in your background that will not allow you to move on. Your experience may have triggered unresolved feelings and therefore you are feeling stuck in your situation. Therapy can help you uncover your issue and resolve it so you can move on.
To find a therapist, ask your doctor for a referral. Or you can search on line at http://therapists.psychologytoday.com/rms/.
I hope this has helped you,