Also, no one said he's the brightest bulb. He's never heard the word home before. You know what, I'm just going to tell you Esper's backstory.
Esper was an egg and his parents were caught. When he hatched, he was all alone. So he waited in his nest until he got hungry, and left to go eat. He was met by some humans after he chowed down on some berries that tried to catch him, but being the clever little Eevee he was, he escaped them. He wandered around, exploring the world around him and learning about many things. Like his latent empathic powers, which had shown themselves since birth. During his travels he met a Glaceon. She taught him how to speak, and other things an Eevee should know. Esper was so happy with her, that he soon evolved into an Espeon. A great many concepts and words hadn't been taught to him when the pair finally seperated. The two of them were set on by humans that wanted to capture them, but they, and the humans pokemon, were then dragged into the reverse world. Esper resisted this with his psychic powers, but he failed, his mind nearly being ripped into pieces. Only because of his empathic power was his fragile and damaged mind held together. The wounds of that are not healed yet. That's why I said not to mess with his empathic powers. Without those to hold his mind together, then he will fall apart and go mad. Does that shed a little light on him?