Ooh, Celegorm... I'm not sure how I feel about him. In my fanon world, he has a crush on Aredhel, which drives him to pursue Luthien. It's rather complicated. In short, he blames himself for Aredhel's marriage to Eol (he doesn't know of her death yet), and Luthien reminds him of Aredhel. In his thinking, Beren is another Eol, and he's bloody well not going to let all that happen again. The irony, of course, is that he ends up trying to force Luthien into marriage, not Beren.

I'm still not sure if that theory works...