As I said, some knowledge of the Silmarillion is helpful to understand some of Haldir's back-story. I wrote up a quick and dirty overview of the Elvish history involved in this story. I have not researched this and so there may be some small errors; it is just my memory of the events that occured in the Silm
If you are familiar with the First Age, by all means don't read this. It's for those of my readers who might like a little background information beyond what you'd find in the text ofThe Lord of the Rings.
The Elves awoke by the shores of Cuivienen, in Middle-earth. Some of them were captured and turned into orcs by Morgoth (Sauron's boss in the elder days), and so the Valar decided to bring the Elves to Valinor. The only problem was one of the Elven leaders (Thingol) disappeared along the way. We later learn that he's making googly-eyes at Melian off in the woods somewhere, but at the time his followers don't know what's happened to him. So some of them stay in Middle-earth until they can find him. These became the Sindar. Celeborn, Thranduil, and Legolas are all examples of Sindarin Elves.
Meanwhile, the rest of the Elves go to Valinor and live in peace for awhile. But things go wrong and, as is often the case ;-), it's all Fëanor's fault. He made three jewels called the silmarils, which Morgoth later stole (and killed Fëanor's father Finwë as part of the bargain). Fëanor returned to Middle-earth to get the silmarils back from Morgoth. But he only took some of the Elves who wanted to come with him in the ships -- those Elves following his half brothers, Fingon and Fingolfin, he left in Valinor to make their own way across. They walked across the ice, and it was a really gruesome affair.
Anyway, in this story I have made Haldir's parents followers of Fingolfin. That means they're definitely Noldor (the group of Elves that went to Valinor but returned to Middle-earth), but they're not Fëanorians. I imagine Haldir and possibly his brothers Orophin and Rúmil being born in Middle-earth in Fingolfin's kingdom of Hithlum, back in the First Age.
Who's Aredhel? She's Fingolfin's daughter. She lives for a while in Gondolin with her brother Turgon but then decides she wants to leave the city. Later she marries a dark elf named Eöl, has a child named Maeglin, and returns with Maeglin to Gondolin (followed by Eöl -- she is trying to escape him). Eöl is told he can't take Maeglin away from Gondolin and decides to kill him instead of letting him grow up around the hated Noldor, but he kills Aredhel by mistake. Aredhel was born in Valinor so is not exactly a cohort of Haldir's, but I don't think that would stop him from adoring her so much growing up that he had a crush on her. She would have been the king's only (named) daughter, after all, so she was probably well-loved by all. That's my thinking at least.