I'll be honest and say that I can't relate to what you did.

Now that is out of the way... I do think you should get some counseling and advise on what underlying issues there are. What is done is done... the key part (and you've identified that you know what you did was wrong) is preventing this happening again in whatever form that might be.

I can appreciate that you're probably beating yourself up over it. You really should talk to a professional counselor (as Gayle suggested) to help you come to terms with the guilt and find a way to move on without repeating the above.