Jen, I really don't think you need to tell your boy anything beyond that you made a mistake and that you're terribly sorry. Do something special for him to make up for it.

At seven, kids still have mean streaks in them that come out when they get angry. He could very well use whatever information you give him against you next time he gets upset at you. That will only make things a whole lot worse.

Even the best of parents make mistakes. You need to stop beating yourself up about it.