How do I label my relationship to my ex, for my son? Do I claim we're "friends", even though we are the opposite?

He's only 3.5 now, but someday he's going to ask a question where I'm going to have to say something

Currently she and I speak as little as possible, and see each other in-person as little as possible. By my choice. I have a low opinion of her as a parent, and as a person (we were only dating a few months before we got our surprise boy)