long term FWB with a couple... is this still casual or have we accidentally built something

so there's a couple i've been seeing on and off for about 18 months now, started as a one night thing met at a club in auckland and we just... kept clicking. we see each other roughly monthly, sometimes more, play but also brunches and the occasional gig together. i'm solo, mid thirties, no interest in being part of a triad or moving in. but lately i notice i miss them when it's been a few weeks, they remember my mum's birthday, last weekend the wife and i got dinner just the two of us. is this still FWB or have we accidentally fallen into something i should name... and is naming it a mistake...