Seth had no intention of revealing the fact that Lena was his mate. When he first met her, he was surprised and taken aback by her striking resemblance to the Queen Fairy, whom he adored a lot while watching the Queen's trials inside the Element Forest. Then, her scent overwhelmed his senses, drawing him in like no other.
He immediately acknowledged the unmistakable Mate Pull which was later confirmed by his wolf, Saul. He couldn't believe how fortunate he was to have a mate who had the physical features that he dreamed of. However, just like all good things, there was a catch. Lena was human and wouldn't experience the Mate Pull like he did.