Presumably Nick wouldn't have tried to split with you, because he'd learned about your personality earlier in the game or was able to gauge your responses as he discussed his certain intent to steal. Nick's ploy was especially good because it put Ibrahim in an unexpected situation where it's a lot harder to appear genuine while simultaneously thinking through optimal strategy, thus giving Nick unusually reliable information about whether he could expect Ibrahim to actually try to split or not.

ETA: Retracted because I'm not sure this is relevant to User:wedrifid's point.