The bold truth
You need to stop feeling sorry for yourself. Fine you made mistake along the way. we all have. Some more than other.But your making it sound like your so old and its too late to better yourself. You can continue feeling sorry for yourself and putting yourself down and when you are really old you are going to be saying this same story about yourself. Or you can change it now and when you are really old you can say a different story, one that speaks of the change you made to your life.
As far as the girl. Who cares about your past. If she accepts it and you make her life that happy then marry her.how can you put yourself down by saying she deserves better when she is telling you that you are what she wants. Let me ask you this if she finds a guy that's had a perfect life with an amazing career yet he doesn't make her happy. Does that make him deserve her anymore than you? If you really care/love her and want to make her happy then give her what she wants not what she deserves
Just because she deserve a better person doesn't mean he is going to bring her happiness