my friend was arrested for assaulting his wife. when he go to the court his wife and him say that they still living together and there is no more

The facts you have included are that the police were invoked in a matter where the husband was charged with assaulting his wife and the couple are raising a child.  The denial at court is to be expected.  Most battered spouses cover up or deny the abuse.  There is a child who is learning this behavior and who is at risk due to the uncivilized behavior of the husband.  Of course the prosecutor and court get involved.  I am surprised they didn't continue with the arraignment and set a trial date.  One can't take back hitting one's spouse, and promises to do it again are hard to believe.