He brought up his ex?

I'm a 22F and he's a 21M. We first started talking 3 weeks ago. the first time we hungout he drove an hour away to pick me and my friends up from the bar to drive us home. i tried kissing him goodbye and he said no cause i was drunk. i've seen him twice since and we have only kissed. he bought me flowers for the third date, has been picking me up, opening doors and being putting in noticeable effort. i know he told his parents and friends about me. My only concern is that during our second date he asked me about my previous ex. i didn't say much, but when i asked about his ex he talked for 5-10 min about how they were on and off for years and she cheated on him. he said he hated her for it. i know this is a red flag, and makes me nervous he's not over her. they have been apart for almost a year. what do you guys think?

He brought up his ex?
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