Well, "porn" essentially is the capturing of sex by video/audio, as just mentioned, so the way I see it, what you'd be looking for would be amateur video.
At the same time, a couple can be 'pretend in love' for the purpose of a professional video. But when looking at it this way, you pretty much are just taking every sex scene between a happy couple in any movie and removing the censoring.
So to me, the closest genres would be "hidden cam" and "R-rated love scenes"