Sorry if I wasn't clear -- with the crackers bit I was referring to this, "My girlfriend, citing the fact that I had accidentally left out some crackers overnight, threw the cereal away". Her using the crackers bit to justify trashing the cereal in the present is shitty since the crackers thing was an accident anyway.

Regarding your longstanding relationship, if you think it's worth pursuing, you guys should probably enroll in couples counseling, considering she wants to break up over this and it's happened in the past and has clearly escalated.

Regardless of her reason (growing up less wealthy, liking to keep things tidy etc.) throwing out perfectly good food on more than one occasional is highly questionable and a dick move.