I’ve been finding that I do use the term “primary” sometimes to refer to my girlfriend, who I’ve been with for longer, used to be monogamous with, and with whom I’m raising a child. What I like about the term is that it lets others know she’s not my only partner, and since we’re not actually married it’s more technically accurate than calling her my wife. But I don’t refer to my boyfriend as my “secondary” partner; I just call him my partner or my boyfriend. I don’t like the hierarchy that the terms primary/secondary imply, and I try not to invite that level of categorization into our lives.