just don't contact her. you felt the need to break up with girl 1 for whatever reason. at that time, she was not worth your time. what makes her worth your time now? what has changed with you or her? what reason would she have to take you back? let's say she actually does take you back for some reason, what assurance does she have that you won't leave her again? even if in your head, you can provide a positive reason to all of these questions, she has absolutely no obligation to take you back. why take back someone who hurt her? nah dude. you need to move on.