One half of your couple makes the other half jealous.
Rodolphus did not deserve Bellatrix.
The Dark Lord was not prone to fits of jealousy – least of all about women, who were apt to bore him and who were not, in his estimation, worth agonizing over – but he could scarcely stand to see Bellatrix and Rodolphus together.
The way he simpered over her was sickening, and the teary, childish look in his eyes when she pushed him away only served to make him look even more pathetic than the Dark Lord already thought him to be.
Foolish man. Useless man.
But whenever he so much as laid his hand upon Bellatrix, the Dark Lord's urge was to curse him, to reduce him to a mess upon the ground, to prove to him without any shadow of doubt that Bellatrix belonged to her Master, not to him.
He disliked feeling that way. He should not – and he did not, did not – feel threatened by one of his own Death Eaters in a matter as trivial as this.
She is mine, he wanted to tell Rodolphus, every time that he saw him with Bellatrix. She is mine and not yours. She will never be yours. So take your hands off of her.