Add me to those who don't get all the references while loving how many homey-feeling details there are in here. Yet, just by reading this:
The story is basically about Arthur broadening his horizons and them (Morgana/Arthur/Gwen/Merlin) forming a foursome. This scene is fairly early in the story, where Arthur pretty much considers himself monogamous with Merlin (the polyamory side of things is all fully disclosed and agreed upon with all involved).

I knew to be ridiculously excited. The way you handle relationships makes me fuzzy inside. ♥