The first one is a dash, not a hyphen. People are lazy and use the same character when typing. In reality there are 3 different characters: тире, знак минуса и дефис.
Here's a great article about typographical nuances: http://www.artlebedev.ru/kovodstvo/sections/97/

Anyway, the author should have used a comma, not a dash, and the second hyphen is used wrong. The correct punctuation would be:

Я задумываюсь, нужна ли я тебе.