Shouldn't need to buy a whole new line. Just pull the flare nut away from the line's flare, cut the flare off (shortens the line by like 1/4"), then remove the stripped flare nut. Go to your local autoparts store and get a new flare nut (and buy/rent a line flaring tool). Slide the new flare nut on, then reflare the line. Your other brake line should have enough slack to take up the minimal amount of length you removed...