Vikram Seth - Mistaken

I smiled at you because I thought that you
Were someone else; you smiled back; and there grew
Between two strangers in a library
Something that seemes like love; but you loved me
(If that's the word) because you thought that I
Was other than I was. And by and by
We found we'd been mistaken all the while
From that first glance, that first mistaken smile.

Vikram Seth

http://www.poemhunter.com/poem/mistaken-23/