When he had heard Entoma had nearly been killed, Ainz’s anger had flared up. Although it had been suppressed in an instant like all intense emotions, in that instant that he had been filled with murderous rage. It was a miracle that he hadn't promptly chopped off Evileye's head with his sword.
He had suppressed his killing intent and not acted on his anger because earlier, he had concluded that killing Evileye would have been counterproductive. At long last he had found an introduction to someone who could use resurrection magic— and they were in a position to benefit from it. Ruining this would be too much of a waste.
Perhaps I've grown, and learned to control myself.
If it wasn't because of Shalltear's brainwashing, it's possible that he would have ignored the potential gains to Nazarick and killed Evileye. The Great Tomb of Nazarick and the NPCs created by his former friends were treasures that Ainz wanted to protect. He would not forgive any attempt to harm them, but he also had to consider what was most important and which choices to make to attain it. That was maturity.
Ainz reflected that his capacity had grown to match his experience, and the illusion of the face underneath his helmet smiled to itself.
At this rate, there’s no doubt that he would be able to become a true ruler of the Great Tomb of Nazarick. Or rather, he hoped to reach that stage.
Before that, I have to avoid disappointing people or suffering great setbacks… it’ll be very hard on me…