Why does Sandstorm like Firestar?

Sometime in the original series. I know that they were in love by The Darkest Hour, and I believe they began to like each other in Rising Storm. They both confessed their love for each other in The Dangerous Path.

Sandstorm at least fell in love with Firestar in book three (Forest of Secrets). Maybe Firestar only fell in love with her in book four (Rising Storm), but Sandstorm had already fallen in love long before he fell in love with her.