Arrested for section 39 common ault?

hi i was arrested yesterday for common ault as i waited for a car parking space this young woman went to drive around my car and go and take the space i had been waiting for when i told her she burst into a torrent of foul mouthed abuse and then spat in my face stupidly i retaliated by spitting back at her.she then went to try and get into my car where my 18 month old son was in the back threatening she was going to hurt him i then pushed her to get her away from the car as i was fearfull of my sons safety. this is the push they arrested me for. i have previous vonvictions from 1992 for drunk and disorderly and 2007 criminal damage i also suffer from bipolar disorder and the thought of a custodial sentence is making me contemplate taking my life can someone please help and tell me realistically what penalty i can expect