Connor did regret that he spared Beth. His policy was to snap the neck of his rivals and kill them immediately before they try to kill him.
That's why a lot of them were scared of Connor as he used to kill his rivals immediately. The only person whom he didn't and couldn't kill until now was Tristan. He was so much more powerful than him.
And now he has another rival who is more powerful than him. Perhaps he made a mistake by letting them to resurrect Ivy. If she had stayed as a corpse then he would have one less enemy to deal with.
But this was all the plan of the prophetess. She was the one who proposed to resurrect Ivy, saying that he could wield her powers. But in the end, he got scammed by her.
He regretted that he spared Beth instead of killing her. But as he slept, he started to
