Sometimes loving someone means knowing when to let go.   On our fourth wedding anniversary, I found a divorce agreement in my husband's safe. It stated that Nathan Carter would walk away with nothing and transfer his company and 1 billion dollars in cash to his ex-wife, Vivian Lane. He would also pay her 10 million dollars in alimony every month.   And what did I get?   I had stood beside Nathan while he rebuilt his business from nothing. We married without a wedding, and he made me sign a prenuptial agreement. I didn't own a single share of the company I had helped save.   "Didn't I tell you not to go through my study?"   I turned toward the man in the doorway. I didn't argue or cry.   "Nathan, I want a divorce."   He frowned, walked in, and snatched the agreement from my hand.   "It's my money. I can give it to anyone I want."   He turned and left without another glance at me.   I calmly called my attorney.