Place it at the end of a reveal, after the evidence has already been shown, then follow it with Awkward Crickets to stretch the moment. For a bigger reaction, put Chipmunk Laugh after the crickets, letting the roommate line stay the setup and the later sounds carry the payoff.
About this sound
This 4.5-second voice clip is the spoken line 'And they were roommates', delivered as a simple statement that lets the implication do all the work. It feels knowing, funny and a little cheeky, like a quiet aside that turns an ordinary living arrangement into an obvious romance. It works because the listener instantly understands what is really being said.