When is it normal and when is it a huge red flag when you are dating someone and they complain about their ex?

To a certain extent I think it’s normal to sparingly bring up your ex when you are dating someone new as long as it’s context. For example there was an acoustic music dive bar I liked in neighborhood where my then girlfriend lived. I went there a few times before I met her. I one time recommended that we hit it up and she told me she didn’t want to because her ex often frequented the same place. That was an understandable reason to bring him up.

But I also remember she was often comparing me to him positively and quite often. While that should be a compliment it also had alarm bells ringing distantly in the back of my head. I am not perfect myself and I am a completely different guy. Sure I am better than him in plenty of aspects. However to I bet there are probably some things he was better than me at. The fact she was verbally bringing this up to me made me very nervous but since it was always positive I didn’t say anything.

Anyway I didn’t take the red flag seriously enough. This girl eventually broke up with me (complicated and I saw it coming). But she compared me to her f*cking ex on the day it happened. Highly insulting and inappropriate. She was youngish (25) at the time but still.

But how much is normal and how much is a red flag when someone does this? I know we are all going to mentally compare the person we date with our past experiences. But when someone verbally outright says too often (even positive comparisons) it’s a huge red flag in my opinion. They aren’t completely over the bad experience they had.

Also to fair I have done this myself to a much more limited extent when I was younger. It’s best to keep your mouth shut about negative past relationship experience out of respect to the person you are dating unless in special circumstances.

Updates
6 mo
When this girl broke up with me she compared me negatively to her ex back then. Extremely insulting.

This all happened years ago. I should have called it both when the positive and the negative comparisons happened. But I never had a woman compare me so positively when things were going well.
When is it normal and when is it a huge red flag when you are dating someone and they complain about their ex?
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