You have to stop beating yourself up about this. You cannot change what has happened and you have made mistakes, and she made mistakes as well. She is not this mindless drone, she is a functioning and capable person and is able to make her own decision. She chose to be with you over her dream school, and if it doesn't work out in the end, she has to accept responsibility for her actions. While she can't help how she feels, she is completely in control of her actions. You did not make her do anything. Cut yourself a little break and stop being so hard on yourself.
Being a person that feels incredibly guilty about everything I do wrong, I can certain sympathize and understand. If you could and would like to go more in depth of your relationship, I would be more than happy to read and offer whatever advice I possibly could to help shed some light on your situation. It sounds like you have alot more to talk about then what you provided here.
Did you really break up with her because of how guilty you felt? Especially as young guys, we all are too common in our selfishness and immaturity. If you recognize this and are instituting life style changes to better help you become a more well rounded and grown person, you are working on yourself. You have to make the effort and not just be satisfied with who you are. I mean you are who you are, but that doesn't mean you have to be a person with glaring flaws. It's possible to change and it should be something you are focused on more so than your girlfriend. She may feel attached to you and not want to give up on her investment in you, but if you guys weren't happy and aren't happy, you made the right decision, even if it hurts so much.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.