Ailill wasn't a rogue earlier. He was a fae who King Ian trusted. But after the war between the faes and the winged demons, the demons were defeated and they were chased by King Ian to their Kingdom, Kingdom of Zor'gan. And the fae who helped the demons was Ailill. It wasn't Ailill's fault, according to Maeve. She was also interested in ruling over Vilinski. However, she had fought with Ian's father in the battle of Sgiáth Bio and had lost. Terribly. And she was killed.
Ever since she had lost, the goddess was living in borrowed bodies of humans only because of Ailill. She was the one who had encouraged Ailill to become an ally of the demons. However, the plan failed and Ailill was banished.
Ailill was declared a rogue fae and chased to the point that he had to go and hide himself in the Hydra Kingdom of Araniea. Often, he would come to Vilinski to meet his mate, goddess Maeve.