Some believe that when Link's Uncle said, "Zelda is your..." before dying in A Link to the Past that he was going to say sister. The last word was cut off from the Japanese translation, with said, "Zelda is your desinty." At least that's my understanding of it.

As far as couplings, I always thought that Link and Malon made a good couple for the Ocarina of Time and Majora's Mask Link. Ruto explained that sages couldn't have romantic engagements such as marriage, which would imply that Link couldn't get together with either Zelda or Saria.

As far as the other games go, I'm not too sure about couplings.