situationship

noun2

1. •
   (informal) A romantic or sexual relationship in which the parties do not consider or are not clear that they are in such relationship; such that is informal, without the responsibilities of a formal relationship; a companionship.

   • The thing about being in a situationship – and this is a big thing – is that because you exist in that no-man's-land, the rules of engagement are not spelt out. — 2016
2. •
   (informal) A person with whom one is in such a relationship.