I think most people hearing someone refer to another just as an Ex, their mind will automatically jump to ex-boyfriend/girlfriend.
I usually try to not refer to or talk about those people much. If they aren't in my life anymore there's a reason for it. If I still have a casual contact then they're "this guy/girl I know" I might refer to them other ways but I don't think I'd just refer to them as an ex without meaning ex boyfriend/girlfriend
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