The boy, young man, says something to the girl like "I will find you... you will find/know me because I will be the saddest boy/man in the world".
The room they are in is a largish, white set where they are all sitting around waiting to be born/have their consciousness transferred into babies.
As I said, it is only a small part of a film that has different scenes/sories/vignettes, may be a woody Allen film, it is of the 70s or 80s era.
Saw it when I was young, 25+ years ago, been bugging me. Any thoughts.?