You know what's funny, and I hope will be explored a bit? Locke told Taryn that the Fae don't love like mortals, but of all the couples in the series that we see with any depth, all of them seem to have the kind of relationship you'd expect. Madoc only seemed to be interested in Eva and Oriana. And that's especially interesting since he and Oriana at least started as a marriage of convenience (I'm pretty sure there is real love between them by the Cruel Prince series). Cardan is one woman at a time kind of guy. He may have slept around while not in a relationship, but it seems like while he's in a relationship he only wants his partner. Even Nicasia didn't seem interested in sharing (although that's rich, coming from her). The Bomb and the Roach are really new as a couple, but even before they got together, there's not much indicating that they are interested in seeing or sleeping with other people. And that's just within this series. Kaye and Roiben don't seem to be interested in Locke's idea of a relationship, either.
As much as people allude to or joke about the sexual habits of the Fae, it doesn't seem to be that common in the story. Sure, we know that Eldred has a lot of lovers at once, and we don't get to learn a whole lot about his other kids' romantic exploits, but Locke seems to be the only one of his circle insisting on it. Even if we assume that all the couples I've mentioned are outliers, it still doesn't make sense for Locke to tell Taryn that his way of being in a relationship is the only way to have a relationship with a faerie, or for her to believe him. I could accept that maybe things were happening outside of the scope of the story, but that's speculative. The actual text of the novels doesn't really support Locke's assertion here.