You are correct in that ABH (if that is the charge) is an “either-way” offence. If he pleads not guilty or withholds his plea at his first appearance the magistrates will undertake an “allocation” exercise to determine where the matter should be heard (this was, until recently, known as the “Mode of Trial“ exercise). Page 201 of this document (Magistrates’ sentencing guidelines) gives some idea of the factors to be considered when making this decision:
http://sentencingcouncil.judiciary.gov.uk/docs/MCSG_Update9_October_2012.pdf
It is difficult to say from your description of events what the decision of the bench will be. But the sustained nature of his behaviour and the domestic background will certainly aggravate the offence considerably. Essentially the Magistrates will need to decide whether the offence, if proved, warrants a sentence beyond their powers (six months custody).
Bear in mind that even if the Magistrates decide to retain jurisdiction your ex has the right to elect a Crown Court trial (but note that he has no right to demand a trial in the Magistrates’ Court if a Crown Court trial is ordered).