I Am The Reason My GF And I Are On Break

I berated her. Called her a lier, said she told half truths, every time she goes out I pick a petty fight.
I know I have self-esteem and a lot of insecurities. How do I get better? How does one go about taking the steps needed to better yourself for the sake of saving a guys first love. And making sure his gf doesn't become just another painful memory.