It's been 9 years... . I'm tired and drained. Does it make me a bad person to want out of this relationship? I'm exhausted from the drama and the constant excuses and the shifting of blame and responsibility. I didn't sign on for a marriage to an adult child that's barely capable of taking care of herself much less our 8yr d. I'm worried and scared about what will happen if I split... . I'm worried and scared of what will happen if I don't split from her.
There are no simple answers to a situation like this.
From your description, it sound like your marriage has grown stale - not abusive - but not a lot of like to it.
Does it make me a bad person to want out of this relationship? This is a values question, so you know better than anyone here. Its a big decision for your little girl. Breaking up the family will be hard on her and you won't see her everyday again - visitation is often every other weekend - some get more. There will be a year or to of battling. You will divide your assets.
Have you tried, with professional guidance, to rebuild the relationship? Would she be willing?