OK I'll break it down for you.
There are nations that are in the EU and nations that are not in the EU.
The EU represents the nations that are in it in the negotiations which includes Ireland. Ireland is not conducting separate negotiations with the UK government over Brexit. It's quite simplistic really.
If you can't understand why leaving the single market means that there has to be customs then there is no point in discussing it.
The UK chose to leave, they weren't kicked out. But yeah, its all the EUs fault and they have an agenda, blah, blah, blah.
I know the EU argument well mate. I just fully reject it and see it as unnecessary and pure profiteering. Britain and Ireland can have bilateral free trade. The EU don't need to be involved.
Explain why Britain and Ireland cannot have a fee trade deal. Why could it not work? I'm still waiting a rational answer.