She looked at me as she did love, And made sweet moan. (lines 19-20)
These lines are usually interpreted as a sex scene. The knight and the lady here consummate their love. At least, they're consummating her love. Notice that she's the subject in this sentence: she's the one doing all the "look[ing]," "lov[ing]," and "moan[ing]."
I set her on my pacing steed, And nothing else saw all day long. (lines 21-22)
The knight is so obsessed with the beautiful lady that he spends the day gawking at her. Is this love, or obsessive lust?
And sure in language strange she said – I love thee true. (lines 27-28)
Again, it's the lady, and not the knight, who's doing the work here. She tells him that she loves him, but he doesn't say a word.