I've been trying to find a movie (or potentially a series or trilogy - I definitely didn't watch the whole thing and seem to recall having missed a movie or two) that I think I saw on the SyFy channel maybe around 2010-2012. All I can really remember is that it was set in a high fantasy world (almost Lord of the Rings, aesthetically) and one of the main characters was this woman (long dark hair, flowy dress I think) who looked human, but was actually some sort of siren-type magical being. Basically, she could ensnare men by making them fall completely in love with her, and I think it was permanent. She had a man she was in love with, but they couldn't actually be together because doing anything together would have placed him under her spell and robbed him of his free will. And there was apparently a way to get rid of her powers, but they were integral to the plot for some reason so they couldn't.
Later, their quest party finds another girl, a little younger, blonde, who's the same type of being with the same powers. Hurray, maybe the first woman can finally be free, at last! There's some backstory where the blonde girl's mother died in childbirth and her father, freed from the spell once she was dead, had his servants chuck her body in the street because she had enchanted him.
So this second girl has a guy that she also likes, but ends up enchanting the first woman's love interest somehow. She's heartbroken, it's no good for anybody, etc. So the blonde girl tells the man to sleep with his actual girlfriend (I think this is the way the dark-haired woman would lose her powers? There was some reason for it) because he'll follow her orders. But the dark-haired woman refuses, because he would only be doing it as an order, and he'd be thinking of the blonde girl.
That's really all I remember. There may or may not be a dragon. Any help is appreciated!