"O! How sweet love must be!" Voldemort spoke in a hushed mocking whisper to the woman who was kneeling before Him with tears streaming down her pretty face. So easy it was to reduce this fierce warrior of His to a broken sobbing child, so easy, too easy, with nothing but words.
Words. They were just words. How was it that simple words from Him could hurt her more than a whip across her back? Bellatrix prided herself on her ability to withstand pain, in fact she could take it better than most men but words from Him, simple, easy words, could either lift her up or beat her down.
And when they were words mocking her love for Him, her adoration and devotion, they cut like a blade straight to her fragile heart.
Did He know how much they hurt? His simple words. How much they embedded themselves in her mind, heart, soul. How she would play them over for hours, days, weeks. Time heals all wounds they say, but time refused to heal the deep cuts of his simple words.
When Bellatrix fell in the battle, she was the last one standing, the only one to not surrender, flee or betray Him, His first lieutenant became His last lieutenant and when He saw her take Molly Weasley's spell straight in the chest over her heart, her delicate, almost broken heart, He knew before she fell He'd lost her. His first, His last, His best lieutenant. So Voldemort screamed His fury (grief) at her defeat, lost now for those simple words He'd never speak to her again.
At least until they were reunited in the after life.