Opening line of
李商隐's (Late Tang)
《无题·相见时难别亦难》:
相见时难别亦难,
东风无力百花残。
春蚕到死丝方尽,
蜡炬成灰泪始干. (Meeting is hard, parting too; the east wind is feeble, a hundred flowers wither. Silkworms spin thread till death; candles weep until they're ash.) The following couplet
春蚕到死丝方尽 is one of Chinese poetry's most famous metaphors for undying love.