Nate... Nate... Nate.... smart man learns from his mistakes.... a wise man learns from other people's mistakes.
My brother... I have been down this road. I have been with many women including chicks like Amy. They always come crawling back... it's just the way it works. You were her rock, she knows that. Unfortunately she views you as a bit of a father figure and she is the rebelious teenager.
This thing with the new guy will get old fast and then she will reach out to you for help.
When she does, politely tell her that your relationship is over and she needs to find support from someone else.
Happy to hear that you are out having fun. You need some alone time. Don't be in a rush to reconnect with another girl. Rebound relationships are usually a disaster.
If you have any questions or need support, I am here for you.
ALSO...
Read the co-dependency book, that will give you some insight into your behavoir. But you are typical Alpha-Male and that is what makes you great. Find a chick that wants a guy like you. They are out there.
Don't do too much self-examination. Your fine, you just got caught up in a bad sitch. Bascially, your a normal guy... maybe a little too nice.