Well, since your girlfriend looks so supportive, maybe you should tell her how you really feel about the situation, explaining that it's not her fault and telling her about your difficult past. You probably did already, in some way or another... but still, a reminder never hurts, right? Also, ask her if she has any ideas on how you can improve!

I hope everything will work out. I'm sure you'll both make a great couple. You just don't have to give up... you have all my support