Most Helpful Guy
I would say so. Any Man who puts his hands on a Woman is a coward and they almost always do it habitually. Women should leave if their guy hits em' even once.
Most Helpful Girl
Yes, the monster will always lie within him /her.. even if s/he gets therapy.
Therapy just helps a person control their anger and aggressive behaviour. It doesn't cure them of it. So they will also have the potential to lose control and start beating again. You never know what situation they'll face in the future which could make them just snap and lash out.
I'd never stay with a beater or enter into a relationship with a guy who beat an ex. Even if he went through therapy and appeared to have "changed", coz I'd always feel I had to "watch my own back" with him.