Once loved? Oh, cherub, if you want to destroy her with the intensity of a thousand supernovas your love is hardly in the past-tense. It’s only through love that we desire revenge, only in passion that we want the source of our devotion to feel pain.
If you truly want revenge, then you will pick up the broken pieces of your shattered heart and you will weld them with molten iron. You will pack that organ with coal, coat it in ice and carve a place for it back in your wretched body. And if after that it still beats, let it pump ice-water through your veins, let it freeze you till you feel no more.
Because if you pursue vengeance, you are just carrying back your shattered heart to her on paper, asking her to light it on fire.