Sex belongs in games more then it belongs in movies. In movies sex often carries no emotional weight. It is there more to sell actors. It is there because everybody expect it. Just after middle part as much needed break before big explosive finale. So in most cases it's tied with pacing of the movie.

Because player dictates pacing in games game stories are broken in small pieces and tied to places or characters . In best case scenario sex in games is connected with a place to designate peaceful or friendly location (The Witcher) or as a ridiculous mini game, silly feature... (duke nukem , God of War, GTA, even Mass Effect as little bigger dialog puzzle). So it is always a place. For me that's missed opportunity to connect with the character, in some other way, and deepen the relationship. Sex in games done right simply starts more questions then in movies. Where is taken for granted just like the world the same movies create.

Let's take one simple example. Half Life 2. Alyx and Freeman. If Half Life 2 was a movie they would probably do it when they enter Black Mesa East. Just after meeting with her father. She is so happy she drags freeman to small room and grabs the wrench. Thanks to her  engineering  skills she takes the  hev  suit off. Freeman (starred by edward norton ) then takes her standing in  typical "suspended congress"  kamasutra  position holding Alyx ( starred by Zoe  Saldana ) ass with black gloves. (For some reason gloves and socks stay on at all times). 
 
It would make sense in movie, but in the game? Stupid and meaningless? Or more  importantly Jessica Alba as Alyx? Are you more interested in relationship between those two characters or Alyx ass? Are we human? Or are we wankers?