If you fail her, I will come back and beat you. What do you mean?

It means that if you fail this woman, both sides will never die.

This sentence expresses deep hatred. Through this sentence, we can also see that this man has deep feelings for women, but women have chosen others. In order to protect this woman, or to be her strong backing, I made this declaration to men.

This is an idiom in China, which means to smash bones into ashes and scatter them on the ground after death. It describes deep hatred or evil.