I'm sorry your feeling so much guilt and possibly shame for past behaviors.
All of us have slipped, some have slipped once and some have slipped many times. We where given the emotion of guilt to let us know we are on the wrong path. That means your a good person, good decent people have the capacity to feel guilt about the wrong. Bad people don't have the capacity to feel guilt, they just make excuses and justify the wrong behavior.
If you are not able to repair this in some way with the person who you feel you've wronged then sometimes we have to forgive ourselves and put it into perspective that you where different then, and you learned a valuable lesson....
This terrible incident has in some way changed who you are, your character and integrity has come out of this for the better. It may not feel like it but the truth is you came out of this a better, caring, and a more mature person today because of this incident. ....You grew and learned, and that's all you can ask for.......And I just know that if you could turn back time you would do different, but since that is not possible, sometimes all we can do is forgive ourselves and move on.....I hope you find some peace with this.....