Guilt is a useless feeling. The people that feel it the most are the ones that deserve it the least, and the people that deserve it the most are the ones that can't feel it.
If you were a bad person you would feel no guilt about the party, so you have already disproven his opinion that you are a bad person.
It also proves that maybe he's not such a wonderful person himself, because he doesn't feel guilty at all for being a jerk.
And the purpose of regret is not to force you to dwell on the past, but to prevent you from doing the same thing again. You can't change what has already happened, but you can make sure it won't happen again. Mistakes help us become better people, but only if we are wise enough to learn from them.