He barely listened as Miles spoke, his mind trying to come up with a way out of this. A way which wouldn't end with his mother dead and the man he loved hating him.
He couldn't.
'Making things up will work once, then she's dead,' he pointed out to Miles. 'And having too little detail while living with the head of the office...? The Lestranges are smarter than that.'
His chest was hurting painfully, and he didn't even think as he took the glass and drowned the whiskey in one go, not even tasting it but revelling in the way it burned his throat. The way it pained enough for the pain in his heart to lessen it grip if only for the time it took him to swallow.
In the end of the day he had to choose. Percy or his mother. He couldn't have both. Either she would die, and everything he and his father had tried to protect would be gone in a flash of green (if she was lucky) or he'd have to betray the trust of a man who never trusted, but who he knew loved him. A man he loved in return. The first person he'd ever trusted and loved enough to care for more than he cared for himself.
How did you choose between the woman you raised you and the man who loved you? He couldn't let his mother die...he just couldn't - but how many more would die if he spied? And when Percy found out...? He would undoubtedly do so and then there would be nothing left at all and Percy too would be hung out to dry.
There was only one answer to this. One way he could do what the Lestranges asked and still not cause their efforts to be in vain. One way he could protect Percy from what would come. He needed to get Percy away from him.
The mere thought made him want to drink himself into oblivion, or curl up in a dark room and not ever get up. Yet he knew what he had to do. Percy simply wasn't allowed to keep trusting him. Which meant he had to break his trust to begin with - and his own heart in the process.