As revealed in EP105 by Nagatha herself, when Nate eventually summoned the bossy snake Yo-kai, the two were married, but they have since divorced.
Yo-kai Watch animation series
Copperled debuts in EP060, having Inspirited Eddie and caused him to become bossy. After Nate identifies him, he runs away and Inspirits Katie instead. Although Whisper advises Nate to summon another Yo-Kai to deal with Copperled, Nate becomes enthralled by the idea of Katie giving him orders, and fantasizes about a future life under Katie's constant beck and call. By the time he rouses from his fantasy, Copperled and Katie have both left - the Yo-Kai having become bored and left his Yo-Kai Medal behind, while Katie left due to Nate creeping her out.