Faelantern is composed of two parts, the Fairy lure, and the Elder tree. The fight starts with the Fairy charming your Sinners, rendering them unable to deal damage even when attacking. You could only ever damage the tree, not the fairy. Its vines will twist and move her out of harm's way. And once the fairy lure's HP has been depleted (so to speak), the tree body will rise up from the ground with yellow eyes burrowing beneath its roots and start attacking you.

What I think, taking the abnormality event into consideration, is that this Fairy acts like most fairies do in game. They charm you into a false sense of security, to feed on you. But the Fairy lure isn't what's going to eat you, it's the creatures beneath the roots that will eat you. Thus I interpret that the Fairy shares a symbiotic relationship with the roots. Without it, the roots would starve, waiting forever for someone careless enough to step on it. Only the roots would get hit when it's attacked, but the Fairy will heal it because it's a known property of the Fairies, they will gladly heal you to procure long term rations.

That's why I think Faelantern symbolises betrayal. These four I have shown here, Sinclair, Gregor, Fajie, and Yoru, all have a significant female figure in their life who has lured them into a false symbiotic relationship and lure them into getting hurt for the Fairy's sake. I still find it interesting that Sinclair resonates with the Fairy instead of the Tree.... Why are you Kromering my boy? That's fascinating.

In a different angle, you could say the Fairy is carrying all that responsibilty to feed the residents of the tree. It depends on her to draw victims in after all.

Interestingly enough as I pointed out in a past post, Lantern EGO gives you horns like a devil. It may be intentional on their part.