I agree with doschicos. My relationship with my ex-husband is like a relationship with a close sibling.
The feeling of affinity even extends to his girlfriend (although she doesn’t feel the same way about me). She’s very prominent in the arts and when people happen to mention one of her projects, I always want to say, “That’s my _____________'s project!,” but there’s no recognized relationship for one’s ex-husband’s girlfriend. Also, it makes no sense to people that I would be excited by my ex-husband’s girlfriend’s project, so I just don’t mention it.