That’s him telling you that he has made exes jealous/insecure in the past. Thinking back, the two men who asked me this were the absolute most toxic partners. They are trying get you to prove you’re the “cool girl” who never gets jealous, even when his shitty behavior is staring you right in the face. This question is asked for a very tactical reason. They will try to spin it so their ex(es) looks like the crazy possessive one, when really, he’s the one following IG models, keeping female “friends” on the bench, etc. These men are a no-go.