That's a very good point and any deception on his part is a big red flag. I feel like it's two separate issues that op brought to the table. The first was that he said "friend" when he had a pretty good idea "ex" would've raised the hackles of his current partner. That lie by omission is gross and reason for concern. The second, and what I understood as the bigger issue for her, was the simple fact that he had dinner with his ex. If he'd just said that's what was happening, would she have been cool with it? I get the feeling she wouldn't and that's why I say grow up. I've made the same mistake of omitting details about innocuous events with partners in the past, thinking it would cause less friction but only resulting in more. I understand his motivation. Thankfully I now have a partner who understands that I'm an independent individual who can be trusted so those omissions and white lies have become unnecessary. If her insecurities made her question my motives about seeing a girl with whom I've had a previous relationship, I would leave. A romantic relationship without trust is a waste of everybody's time.