Kate definitely had a crush on John in high school but they only became a couple after Judgment Day.

Han and Leia...hard telling. But there was plenty of UST so probably.

Mac totally had a crush on Christine when he was partnered with Stan but he loved Claire and wouldn't act on it. Ditto the inspector...he kissed her but that was it. He was too faithful to cheat.

Ax so had a crush on the female Andalite in The Arrival...Estrid. Til he found out she was a traitor who wanted to help her crew mates release a virus to solve the Yeerk problem by killing humanity. After that, forget it

Luke had one on Leia. Probably later he had one on Callista (yuck) before they fell in love and I say possibly Mara in a way. Before the Force cemented things anyway. More UST lol

Callista annoyed the hell out of me. She really had a hangup about Mara being around Luke, when Mara wasn't remotely interested in Luke

Nod. That was only later