Guilt is something I've lived with over my entire life, and I understand how damaging it can be to one's psyche. If you're someone like me, an eternal pessimist, it can be downright damning. The trick is to realize that the present is the only thing that you can control, and that whatever happened in the past can serve as nothing more than a lesson to be learned, as you can never change it. Coincidentally, I just shared a line from one of my favorite movies, "Hector and the Search for Happiness". The line is, "Nostalgia isn't what it used to be". See, the main character of the movie is filled with thoughts of "what if I had done things differently?" and he ends up meeting with someone from his past who essentially tells him that his idea of the past is irrelevant, because the present isn't the past and it never will be.
You can't change it, so it's better to hold onto those memories of past wrongs in a way that will help you avoid those mistakes in the future, but not in a way that keeps you rooted on where you went wrong. Life is going to move on, with or without you, and it's better to go along with it.
Best of luck to you, and I hope you can overcome. Many of us go through moments like this, but they're definitely survivable.