Why is life so hard sometimes?

Why, when I'm not the one (the only one) in the wrong, does it feel like I am the only one who ends up feeling horrible? I did something really stupid last night. I got really mad at someone in front of other people and showed my anger inappropriately. It wasn't uncalled for necessarily, but the way I acted was horrible nonetheless. However, when I tried to talk to them, they didn't want to have anything to do with it. Which made me feel even angrier and just worse all around. But When I was able to talk to them tonight, they apologized and said they felt awful, even crying a little. This made me feel horrible. So we apologized and hugged and made up, so why do I feel bad still? Is it because I know things will still be the same? Or because I know I genuinely hurt someone with my actions? Or because it was just a bad situation all around and people, including myself got hurt? Why is life so hard sometimes? This seems like the simplest thing...you hurt someone, apologize, and then everything is fine. But that isn't always the case. And I don't always know why. I wish I had someone to teach me all these things. But that's another story. Because I know I do; lots of people I am just a hard-headed student who chooses not to listen.