The Police do not normally charge a person with Common Assault, choosing instead to leave action to be taken by the injured party themselves.
However, from how you describe your injuries it would seem that at the very least your ex-boyfriend should be charged with the offence of assault occasioning actual bodily harm, which carries a sentence of' imprisonment. But this is rarely, if ever, imposed. It is impossible for anyone on here to advise you as to the actual sentence one might expect in any circumstances since much depends upon the circumstances in which the offence was committed, whether the offender is of previous good character, whether the injured party contributed somewhat towards the commission of the offence, and what attitude the offender displays at his/her trial, ie does he/she show any genuine remorse ? And, equally important in such matters, are YOU likely to stick with your story about the events, or are you likely to retract on any issue ?