The open relationship thing makes sense in the sense that when James was kissing Stefan like that, my first thought was would William not be a bit pissed off at home seeing that but if they had an agreement... But could Stefan and James also just be over-affectionate friends? I’ve seen girls on nights out giving each other pecks on the lips. And we never see William with other boys but then he does share less online.
They do seem to have separate groups of friends that don’t really cross over which is healthy I think. William’s seem more artistic while James’ many many different groups of friends seem more extroverted and influencer types. I’d find them exhausting to be honest, I don’t blame William for going out with his own circle.