Could it be the ring talking to Isildur?
My treachery leads to your great deeds - Isildur did a great deed in defeating Sauron
I've broken your family, then protected you from harm - Sauron and the ring killed Elendil and indirectly Anarion, then at the Gladden fields Isildur was protected by the invisibility that the ring provided
Because of me you safely escaped, because of me you had to - Isildur escaped the fight at the Gladden fields and was forced to in order to keep the ring from fallin into enemy hands
My protection lasts only tonight - The ring protected Isildur only until he initially escaped, and then abandoned him to his death
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