How is it so easy for girls and a nightmare for boys?????

I had a girlfriend whom I loved with all my heart. I am sure she love me with what she had too. The intimacy we shared was blissful. We have had several misunderstandings. And most of the time I am guilty of having derided her with profanity. But then, I never knew all that will result in our split up. She had an ex-boyfriend and her pals told me she never gave him a reason for their split up. I asked her the same questions and she always comes up with unconvincing replies. A few months ago she told me she has decided not to love me anymore and the day she told me this, she got back to her ex-boyfriend!!!!!!!!!!!!!!!!!! I mean, I am absolutely amazed as how do girls forget all that and get into a new relationship. All I am left with now is guilt, pain and shame!!!!! I feel miserable. Of course I am to be blamed for have treated her with contempt sometimes. But don't tell me that provoked her to leave me and get back to her ex!!!!!!!!!!!