Oh, I meant in terms of how the two previous commenters in this thread defined cheating.

Personally, I don’t think flirting is cheating. This guy feeling the need to lie to his gf about the true nature of his relationship with his ex indicates that their boundaries are different, and we can potentially assume that he’s disregarding hers... all of which is shitty. But we also aren’t privy to the rules of this guy & his gf’s relationship. Appearances (gf seemingly traditional) can be deceiving, and OP hardly knowing the gf doesn’t really help. Neither’s boundary/definitions of cheating are inherently wrong, but if they aren’t on the same page, that relationship’s not likely to go well. The guy’s gf deserves honestly and both deserve a conversation about where they stand with all of that.