The dog ate my homework too.
Apologies, couldn't resist. But in all seriousness, that is EXACTLY what this story reads like.
Whatever course of action you decide, you are going to have to close some of the wide open gaps in between the lines here, which are all too easy to read into. Perhaps the wrong way, perhaps not.
I don't doubt the animosity of the ex and her friend towards you (I know all about that). Nor do I doubt their surreptitious intentions towards you (I know all about that too). And I certainly do not doubt the attitude of the bouncers.
But what you have to realise is that we have all heard this before on here. And so has the magistrate. And the cops. And the lawyers who will hang you out to dry at the expense of your hopes of getting off. And here's the interesting thing... with what we have heard before, EVERYONE says exactly what you are saying.
Is there some kind of loophole here the police are exploiting against us legitimate, poor unfortunate victims, who managed to get pissed in half an hour because of bad shit that happened literally just before - in a pub at 01:30 in the morning I should add (no, absolutely nothing fishy about that) - where we have admitted to consuming alcohol, just not as much as they say? And where (again admittedly) it has kicked off and you and you alone have been ejected (rightly or wrongly)? Yeah right.
Even you have to admit this really doesn't look good. It's all too convenient. And that is exactly how it will be viewed by a beak who sees this shit every... single... day.
The case before mine was a DUI. The case after mine was a DUI. Seriously they have heard it ALL BEFORE dude.
Whether or not you've been done up like a kipper or you're lying matters little really. The situation is real. You have two choices therefore - find better, solid proof that you were not drunk when you left the place in the early hours having admitted drinking Guinness and apple chasers (oh and buying lots more Guinness but not for you, obviously...), or just swallow it and take the punishment. Like 99% of us on here were strong enough to admit and do.
I don't blame you for looking for a way out of all this. Especially if - somehow - there is truth in what you say. It's natural to with so much at stake, and we all have our reasons.
My advice would be to make peace with the bad company you keep, implore them for help, it seems your only choice here opposed to doing the other obvious thing in just admitting your guilt. And after that, keep better company in future.
Regardless, I wish you the best with your situation... whatever the truth of it all is it must be hugely distressing for you. But just know that no magistrate in the land will look fondly on a not guilty plea that cannot be substantiated. You will only make a bad situation worse.
Good luck.