la belle dame sans mercihow did the lady showed that she loved the knight
It is clear that the mysterious lady gave every appearance of loving the knight through her body langauge and what she said, if you can consider the "sweet moan" to be language. However, as #2 makes clear, it is pretty obvious that this is just an act of the lady. She wants to lull the knight into a false sense of security so she can seduce him and lure him into the trap which so many other men have fallen. Keats gives us an excellent image of a femme fatale in this poem that seeks out and tries to ensnare gullible chivalrous males with her charms.
"She looked at me as she did love,/And made sweet moan" is interpreted by the knight as the lady's indication of love. However, "as she did love" really means as if she were in love; so the lady is really not in love. She simply feigns love and seduces the knight by giving him "manna dew" and tells him "I love thee true."
As the poem concludes, the reader realizes that the "faery child" has merely lured the knight to the same place that the other pale knights are doomed to be.