‘I still haven’t paid him back.’
THAT'S who hes obliged to: Nikolay, for getting him back to America; doesn't matter if he slept with his wife. Was this why Pyotr was negotiating with Nikolay over Shatov? Because initially, Nikolay has power over him, and Pyotr wants the benefit of Shatov having potential for a printing press
If this is Shatov's case, then Kirillov must be in a similar position