Is he in AA? Unless he is actively working on his recovery in some way (AA, SMART, or therapy for example) he will be a lousy human being to be around. and resentful of everything.
I feel really bad for your son. There is little value for him in this experience and it may be damaging in terms of learned behaviors. I went through it as a young child but my dad was rarely around (worked overseas). He was always drinking, which your ex may or may not be, but in any case I'm sure your son is tired of the unpredictable behavior.