the opposite of love is not hate, it is indifference. the fact that she wrote this letter does mean you still own her. great success.
Very true. Don't send some hate filled reply back, the best thing you can do at this point is not respond back. It will leave a flurry of possibilities in her mind as to whether you received the letter as well as have her wondering why you never responded then back to thinking you may not have gotten it.
Last sentence about fucking 3 guys may be true but more than likely just jealousy plot.
The best thing you can do is not respond, indifference would be an epic move in this case.
