Im still in love with my ex boyfriend  though he's married now
That's something real considering the fact that an ex is someone with whom a person was once associated, in a relationship, marriage, or once talked to
Yeah!  But I still  love him, even if he's  my ex
Anyways, can refer to a variety of different relationships one might refer to a music group's "ex-guitarist
Ok, not only boy or girl friend  relationships 
It depends, if it is used as a noun and not a prefix yes. As a noun it refer to a former sexual or romantic partner
OK that's  quite thoughtful!  What other forms is it used?
spouse. This often has a derogatory tinge, especially if it refers to unrequited feelings.
Ex (relationship)
In social relationships, an ex (plural is exes) is someone with whom a person was once associated, in a relationship or marriage. As a prefix, "ex-" can refer to a variety of different relationships; for example, one might refer to a music group's "ex-guitarist", or someone's "ex-friend". 
When used alone, "ex" as a noun is assumed to refer to a former sexual or romantic partner, especially a former