Are now you're asking !First of all you must choose trial by jury. The magistrates court trial is an option for you but not one you should take .
In the end it will depend on what the jury feel about it.They'll see the complainant and any witnesses, they'll see you and if they think it was six of one and half a dozen of the other, or might have been so or they are really not sure that you were the attacker or not sure you were going beyond what was necessary and reasonable to defend yourself, they'll acquit.
Self defence is using reasonable and necessary force to defend yourself. But .the judge will direct them to apply common sense to 'reasonable' in self-defence. If the jury think that, under attack or the imminent threat of it, you , 'in the agony of the moment' used no more than appeared to you, a normal person, to be reasonable and necessary force to defend youself at that instant, then that is the reasonable self defence. It may in fact, have been more than was strictly necessary but common sense dictates that someone in that position can't weigh to a nicety the precise degree of force needed.. They can hardly halt, step back, and consider exactly how hard the blow needs to be to save themselves or in your case decide whether a bite is just enough or too much!
Being drunk doesn't help you. It doesn't provide a defence , obviously,but you must accept that people take offence more easily,, do things they wouldn't do sober. On the other hand, the other man was not likely to have been stone cold sober either and may well have felt unusually irritated by you, such that he would hit you,. Your counsel will know how best to deal with this aspect.
Your case sounds very 'runnable' as counsel say, but it's quite impossible to predict or say how well it will go . We haven't seen the evidence, after all. You should definitely plead not guilty, on what you say.