Emphasizing secrecy and quietness:
* A breeze rustling through dry leaves.
* The silent murmur of a stream.
* A moth's soft wings brushing against a flower.
* A secret shared between shadows.
* A whisper of a prayer carried on the wind.
Emphasizing intimacy and closeness:
* Two souls dancing in the moonlight.
* A shared secret held between two hearts.
* A love letter written in the language of the stars.
* A gentle caress of the wind on your cheek.
* The soft touch of a lover's hand.
Emphasizing fragility and fleetingness:
* A snowflake melting on your tongue.
* The echo of a forgotten dream.
* A ghost's soft sigh in the night.
* A fleeting moment captured in time.
* A fragile promise whispered on the wind.
The best metaphor will depend on the specific context and the tone you want to convey.