The story of the sunflower
Once upon a time a water nymph called Clytie was immensely in love with Apollo, She would watch him with unblinking eyes as he moved across the sky. He looked all the more handsome to Clytie. Unfortunately, Apollo ignored Clytie and never returned her love. But Clytie continued to watch Apollo as he passed through the sky. She sat on a rock for nine days without food and water and just kept looking at Apollo as he passed in the sky. Eventually, she was turned into a flower, which came to be known as the Sunflower.
How great love is! So sunflower says silent love.
If in reality you can't go to express your inner feelings , send him/her sunflowers or jewelry with sunflowers :).