I mean, technically this could apply to watching any show or movie with a lot of passionate sex-doing in it, but COME ON IT'S THE AFFAIR AND THAT'S WAY HOTTER THAN WHATEVER NICHOLAS SPARKS SHIT YOU GOT.
Whoa! New person in bed with you and you're kissin' WAY hard and you both know where this is goin' - a one way ticket to genital-mash city. The excitement of a new person, the adrenaline of not knowing what kinda hand stuff they're into, and the unrelenting terror that you're WAY WORSE at this than literally everyone else they've ever been with.
After a while, any sexual relationship can get a little stale - so both partners make an active attempt to spice it up by trying new uncomfortable positions, wearing new uncomfortable underwear, and sticking things in new uncomfortable holes.
Whether you're AirBnBin', at one of your parents house for the holidays, or staying in a hotel for a wedding and/or vacation, there's something incredibly erotic about the idea other people can hear your gross sex grunts (and knowing you won't be entirely responsible for cleaning the sheets afterwards).