Assault on a minor and 50 b?

My ex and I are currently battling for custody.my children have resided with me solely since we separated almost a year ago. I just filed for child support and he is trying to get out of paying because he has his girlfriend and her 3 kids living there. My ex went to the magistrate and filed assault on a minor charges and a 50b against my current boyfriend. My boyfriend slapped my son in the face after my son was name calling and hitting him and his brother repeatedly. My boyfriend never harmed my son but the child's father greatly exaggerated the claims. My boyfriend has been in the military and has no prior criminal record.he is greatly concerned that this will ruin his chances of re enlisting and becoming a police officer. Does anyone know how seriously they take the charge and how difficult it is to get the 50bdropped?