Originally Posted by bofish
It fits most into primary/secondary...but different in some respects. It seems in that model, falling in love is off the table?
The first and second examples of primary/secondary in GG's link show NSA / swinger relationships, which usually forbid emotional connection. The non-swinger example was doing well until it used "falling in love" as the trigger for demonstrating a veto rather than something else like substance abuse or non-specific heebie jeebies, but it was an example showing how veto applies to the structure rather than of the structure itself.
There's no checklist you have to fit if you choose to label yourself; it comes down to what the people in the relationship have agreed to. If the people in a primary/secondary relationship agree that falling in love is ok, then falling in love is ok. If they agree that they'll only eat strawberry icecream together then eating strawberry icecream with others is not ok unless they first renegotiate the boundaries. In either case someone on the outside is within their rights to decide that they don't want anything to do with that type of set-up and move on, but the boundaries a couple set for themselves can be anything.