I think Sarah and Will were intially just friends that cared for each other and maybe it developed into young love at an early age.

But I think that the author just left that out of the story to keep the story focused on the issue at hand. I for one would have enjoyed a little bit of romance. I do think Will was very good for Sarah. What would have happened had Will not pushed the issues he noticed and shared with his Mother. I think Will and Sarah's love devloped from this caring attitude that Will had.