[dancing spawn of ungoliant]

just a little thinggie that you can ignore but Glaurung told these things to Nienor/Níniel and then she killed herself. Turin heard those things from Brandir.

and about the original question, why Túrin killed himself, i would like to add that he had lost mother, father, two sisters and his child and he had killed an innocent people( =Brandir, i don't count Beleg 'cause it was an accident).
what a happy life!