Relationships are one
If you think about it, there’s probably more distance between the kind of relationship you have with your parents and the one you have with a random friend—both considered personal relationships—than between the latter and one with a colleague you get along—which are considered a personal and a working relationship respectively.
Designer Massimo Vignelli famously said “Design is one”. in the sense that the principles of design apply to all design disciplines. In a similar way “Relationships are one”, in the sense that the principles of human relationships must be the same for every kind of relationship between people.