Hey DGuy,
I don't know if my post will give you any valuable advice, but I just want to tell you that I know how you feel. In fact, I think I am the female version of you. Similarly, my ex boyfriend treated me like I was a princess when we were together. I, on the other hand, was much less kind to him. But I wasn't mean to him because I didn't love him, because I loved him like no one before him. I think back, and I realize that I was unkind to him because I was afraid to lose him... I know this sounds insane, but maybe you'll relate... My rational was: if I'm mean to him, I wont love him as much so when he dumps me I wont feel as hurt. I guess I was scared to really love someone, so I set myself up for disaster from the start. Now I'm full of regrets and I wish I could have done things different, much like yourself...
My advice to you is to figure out why you treated ur gf badly in the beginning. Are you really just a bad person? or were you acting badly to her because of a more complicated reason. If you figure out the answer to this, you can tell your ex gf about it, and maybe she'll see that you really did put time into thinking about ur past actions... Maybe she'll even give you a second chance.
Good Luck anyways... Cheers