Definitely regret. It stays with you for a long time. There are things that I regret doing or saying that have happened years ago and I still can't get over it. Regret ultimately leads to guilt and the two are intertwined. Rejection to me is like a walk in the park. If I get rejected by someone, I eventually get over it and move on. I know I am not the one at fault and wouldn't waste my time hating on myself. But if I was the one who caused the hurting, I would feel regretful and guilty and that my friend would be the worst feeling in the world.