"How dare you, you bitch!?"
Malcolm did not hold back from ridiculing her the way she did. He directly called her bitch despite knowing that she was Kayden's mate. Due to the link between the three of them Malcolm was also able to sense that she was Kayden's mate. And since he was just a mere blood servant for him, thus he was obliged to respect Lydia just as Medusa.
But perhaps he was also unable to force himself to respect her the way she acted all high and mighty in front of them. It was not like she could not feel the same link, but Lydia chose not to pay heed to that strong feeling.
Malcolm leaped towards her but before he could use his speed to reach Lydia and to strangle her, the succubus stopped him by grabbing his arm. Medusa could not afford to offend Kayden by attacking his mate, even if she was deeply hurt by the realization.