After being carried out of the nightclub, Rob ends up staggering around on the streets until he gets picked up by a Garda car and taken to a nearby station where he's thrown in the cells to sober up. His shoulder is still killing him. Last time he went to a physiotherapist he was told that it was psychological, an old injury playing up in times of distress. He'd nodded along and hadn't bothered to go back for the follow-up appointment.
He must drift into sleep at some point, despite the noise from the surrounding cells, because he awakens suddenly, scared and uncertain, in an uncomfortable position. It reminds him of those nights at school when he would wake up, screaming and crying at some unknown terror, sometimes having wet the bed. He's grateful that he hasn't pissed himself, at least.
He's still a bit drunk from the night before, but he manages to gather his wits, enough to bang on the door and show his ID from his pocket. He sees the Oh shit look on the young Garda's face when he realises he's locked up one of his own, but it's not like Rob is going to tell anyone about this. He can just picture O'Kelly's face.
Released quickly and sent on his way, he arrives home as dawn is breaking and finds all his belongings on the doorstep, with a note attached in Heather's familiar handwriting, like one of her fridge notes except this one just says "FUCK OFF, ROB". He takes this as a clear indication that he's not welcome there and so he throws the bags in his car and drives to his mother's.