When is enough enough with supporting stepkids?

I have been married 7 years and she had 2 daughters when we married. Ok I never wanted kids but I will tolerate it. Well a year ago the 15 yo gets pregnant. This wouldn't have happened if my opinions mattered. And now my wife is trying get guardianship of her handcapped daughter that her parents raised before her fathers passing. All this for the most part is becoming a burden I have no say so but have to pump out the bucks for support and I am now going broke, insane and miserable. Just feel used and just want to run with my clothes and never turn back. Any advice?