To be as short as possible I'm gonna shorthand a little. Married 2 years, together 4. I have daughter (11) and wife has daughter (13). It's been extremely difficult living with stepdaughter as she has been very difficult her whole life. Her mother is bipolar and has been hospitalized for it at least once while married and is finally on meds and mostly stable. Bipolar is Something I didn't quit understand until being with her for a few years. Never even knew what it was. Father has never been in picture and stepdaughter has been shuffled around to grandparents and great grandmother her whole life mom apparently was a partier early on and then worked a lot to support SD. Boundaries don't appear to have ever been established with stepdaughter. She is 13 now and has always had extreme meltdowns when she doesnt get her way and they are getting worse. She wants to be treated like a 16 year old but is as mature as an 8 year old. On top of it all I believe she has bipolar as well. The entire family especially me, has to walk on eggshells to make sure we don't upset her. This could be anything from, "please do your dishes"' to correcting a dicapline problem. Her most recent meltdown was due to being asked to carry her own stuff from the car to the house like everyone else (By wife) Nuclear meltdown, and CPS called.  Obviously they saw through it and talked her off the ledge.  Next morning wife takes SD phone while asleep (wouldn't give it up day prior) and another meltdown occurs. This time SD refusing to let us leave for work( blocks door) and dumps my wife's drawers and jewelry box all out on floor in a rage. At this point no one feels safe around her and we were certainly not going to physically move her out of the way. SD completely loses it so wife decides only safe thing is call police. They came and saw how she was acting and took her to hospital where she stayed for a few weeks. (Moved to behavioral health facility) Treated for mood disorder possible bipolar. She does not have phone anymore, on meds kind of stable as long as no one upsets her and in counseling. This is a nightmare and I don't know how much longer I can do this. I can't ask her to nicely do anything(pick up her stuff for example) without meltdowns.  She moved in with her grandmother and is with us on weekends and that has helped. Wife and I fight very little and the house has become stress free. She does come to visit and all I can do is stonewall her to just stay out of her space and not upset her. I'll admit I  don't want to deal with her either.  She has mostly been fighting with wife and I occasionally speak up when it's gotten out of hand and she is being disrespectful to her mother or crossed the line.  I don't want my daughter learning any of this behavior and don't think she deserves to live in a terrible environment. I have gotten so resentful towards SD and just waiting for the next meltdown and fight with wife who is in mommy protect mode and has lots of mommy guilt from before we met (worked a lot so not home) dad never in picture. She definitely has discipline issues but wife just blames it on SD behavioral health issues.  I feel terrible saying this but I'd be ok if she moved in with grandmother full time and left for good. My wife obviously loves her unconditionally so it doesn't matter what SD does. I just can't do that and I don't know why. I've never felt this way towards a person and my wife sees it. Our life has been miserable until SD moved out. Not perfect but much much more calm and stress free. I think wife will get resentful towards me for SD moving out. Again I feel like a terrible stepdad for disliking my SD but that's where I am. After last meltdown she is so unpredictable and I wanted her out. 
 

I know I could have  a good effect on her (as steady male figure in life) and I see it when she lets me but these meltdowns are pushing me away.  I cringe when she is around and the whole atmosphere drops in family. She is very selfish, lazy, jealous, immature, entitled, extreme mood swings, disrespectful, lies, yet can be sweet when it benefits her and has her mother wrapped around finger. Knows what to say to invoke mommy guilt. Underneath I feel like she is sweet but has had such a disrupted life and have blamed my wife and her family for SD being like this. This was a terrible idea and should never have been said.  I'm feeling so defeated because it's out of my hands ( per my wife) and have to just sit and watch this terrible and completely consuming disruptive behavior when she comes over. Wife agrees she has always been difficult yet is mommy guilted into catering to SD every time. Wife is also trying to force me to love SD.  I feel bad behavior and mental health issues are to blame but is she too old to teach? She needs to learn the basics you teach a baby unfortunately.  Am I alone here and is there anything else I can do? Hate is a strong word but I'm getting there sad to say.