I've been lying to my girlfriend of 4 years that I cheated on her 5 months ago.
Don't you think you should come clean about what you did?
She would be hurt if she found out that I cheated though.
While it is understandable that you would want to keep your girlfriend from knowing that you had cheated, it was wrong to cheat and then lie to her. You have broken her trust twice, and she is unlikely to trust you again. You should sincerely apologize and promise to change.
I'm not sorry. I enjoyed it.
If you don't feel bad about cheating on your girlfriend, then you should end the relationship. You are only going to cause her more pain by continuing to lie to her and maybe cheating on her in the future. End the relationship now so you can both move on.