In the historical/literary version, she kills herself because they are on the verge of total defeat - are trapped and surrounded - and she doesn't want him to be distracted and weakened by his love for her but instead to concentrate on nothing but battle. It doesn't work - he cannot win after all and kills himself rather than escape. Chirpy! They are kinda the ultimate doomed historical OTP. I like her because apparently she refused to stay at home and rode with him into every battle which is pretty badass :)