Have you had an Ex? I can tell you that is someone with whom a person was once associated, in a relationship, marriage
I have had an ex.  she was crazy!  Have you?
I have had ex friends, It depends on how you define it though because can refer to a variety of different relationships
True.  I was just thinking of an ex girlfriend.  I guess I have a lot of Ex's then.  Ex friends, ex girlfriends, ex employers, etc.
Well, let me tell you now that in social circles and noun is assumed to refer to a former person you have had sexual relations with