I think the only time (except, maybe, for some Marvel comics) I saw any hint of a flirt between Luke and Leia was the final lines of the A New Hope novelization...

"As he stood awash in the cheers and shouts, Luke found that his mind
was neither on his possible future with the Alliance nor on the chance of
traveling adventurously with Han Solo and Chewbacca. Instead, unlikely as
Solo had claimed it might be, he found his full attention occupied by the
radiant Leia Organa.
She noticed his unabashed stare, but this time she only smiled."

And I bought that book in the middle 1980´s, I don´t even know if the movie novels had parts retconed later...