All signs point to Jareth, the mid-40s Goblin King, being in love with Sarah, who can't be any older than about 16. Since most girls who watched the movie back in 1986 thought that was super romantic and awesome, nobody really considered that Jareth is actually a worldly, supernatural predator with a not-so-healthy obsession with a minor.
If you take into account how Sarah, at points, seems to reciprocate some of Jareth's attraction, you're in a Humbert Humbert/Lolita type situation, but nobody cares about that, because, well, Bowie. Heck, what human wouldn't want Bowie to be in love with them?
The Goblin King's intentions are pretty wack, too: "Just fear me. Love me. Do as I ask, and I shall be your slave." No thanks, Christian Grey. Don't think we'll be signing that contract.