Swap on LetMeJizz
Four people splitting into reshuffled pairs, partners handed off mid-scene, is the image the whole tag is built around. It runs two ways, couples trading partners by agreement and step-family setups where two households cross their young-adult members over for the night. The camera works the room, cutting between both couplings so you see who ended up with whom. Half the charge is the moment of trade itself, the look exchanged right before everyone pairs off with someone new.
121 swap videos here, all HD and all free. New ones go up daily, so check back if you don't find your scene first time around.