I hate to break it to you, but romance dialogues are based on REAL time (as in REAL life). So no matter how long you sleep they only trigger after a certain amount of real time.
If you're strictly against cheating (which would be SO much easier
) there's one trick most people use:
1. Pause the game
2. Watch a little TV, fetch yourself something to eat or just go out buying groceries
3. When you come back after some time unpause and the next dialogue should have triggered.