Same for me. As long as I'm not married, I'm single.
'Relationship' is a very generic term that seems to mean whatever a person feels like at the moment. Look it up in the dictionary - you are in a relationship with your family, your friends, your pets, your coworkers - everyone you ever interact with. Anytime someone uses the word 'relationship' to mean something more specific, they are making up their own definition and you'll just have to ask them what they mean by it.