What is repentance?

Repentance means walking back the states of mind the led you to sin. It means setting yourself the task, in Christianity with the aid of the Holy Spirit, of ceasing to be the kind of person that committed that immoral act in the first place. That is no fun. Sinful acts are attempts to satisfy sinful desires, and repentance involves undercutting the grip of those desires on you. It's supposed to be painful. The idea that "Oh, I can sin, and then just repent later" is a self-defeating one. It's something that will make your life tougher in the long run.