What your cousin did was help me, Bellatrix. He discovered the key to your masters weakness, and he left it where I could find it. I did so, and I killed your master. Just so we are clear. I'm not ashamed of what I did, although I would have been happier had he never started his war with me.
He did destroy you Bellatrix...I can't show you, and I know you won't believe it, but in my time, he did.
And I never doubted you loved him. But I don't think a love that sends your beloved on a path to eventual destruction is the best of worlds.