Daeron isn't creepy, or at least he shouldn't be. Recall that originally he was Luthien's brother, and shows little to no actual romantic feelings for her in the earliest versions. If anything he's concerned. That's going to be hard to communicate for us, since we've made Daeron and Luthien romantically closer than in those early versions, but I think in the end he is at worst jealous and impulsive. He is creepy in that moment maybe but should not be portrayed that way overall. No matter how we do it, I think Daeron ought to repent more clearly. Perhaps he could aid Luthien in her escape before he leaves? Just a thought.