What would you do in this situation?

I am at my wits end and am ready to call it quits on my marriage. My 15 yo step-daughter is out of control. She curses both her father and me out any and every chance she can. She succeeds at manipulating her father to do whatever she wants and buy whatever she demands. Defiant behavior abounds. My husband, while fed up with his daughter's behavior, constantly defends her and her bad behavior and attitude to any and everyone. I have had so many talks with him and state that I will not put up with her language and defiance anymore. My own two daughters, while not perfect, are certainly respectful and polite to me and to my husband, their step-dad. It's gotten so bad that I am sending my oldest daughter to stay with family out of state for a few weeks so she can relax and enjoy life. (She is disabled and dependant on me 100%) My other daughter is away at college. I've already told him I am moving out. Now all of a sudden he wants to talk things thru. Been there, done that before with him. Will listen again but I just want peace back into my life. He accuses me of having affairs and hiding finances and other things, all of which are very untrue. He even has his 15yo accusing me of affairs. Second marriage for both of us and I'm ready to wash my hands of all of them and live the rest of my life alone just to have peace. Am I missing something here? Is asking for respect too much? I have not been disrespectful to any of them and have held my tongue plenty of times, but I am fed up with all the drama. Plenty of people have seen them in action and are left with their mouths gaping from shock. Without this step-daughter around, her dad and I get along great. She obviously has emotional problems and is home schooled due to bullying others in public school. She dishes it out plenty, but cries poor pitiful me when others stand up for themself. What in the world can I do to get this kid straightened out without jeopardizing my marriage to her dad?