This is a reverse hidden word - look for letters hidden within other words in the clue, but read backwards.
The phrase 'sent back' indicates reversal. Look for letters hidden within 'the-love-that-dare-not-speak-its-name' and read them in reverse order.
Answer: STONE | Hidden in reverse in 'darE-NOT-Speak' - taking ENOTS and reversing it gives STONE (an engagement ring stone symbolizes intention to marry).