i love her but she leaves me

Maybe she did not love you. Love must be both ways for a relationship to work. You can't generalise about girls or boys and say they are all bad just because one relationship did not work out. People are individuals. One may be bad but that does not mean all are bad. I have loved men who left me but we talked about it and they did not love me the way I loved them. They were looking for someone they could love. We were good friends but it is not enough for a relationship to work.