I am at my wits end! Hopefully there’s some big advice out there for me! I apologize in advance that this is long, but I am really in need of help and want to get all the pertinent details out.
I am in a live in relationship with my SO. We have been together 18mo, and my 14yr old DS and I moved in 6mo ago. My SO has two daughters, SD20 (whom I adore, but she lives on her own) and SD14 (who lives with us and I’m having major issues with). SO has full custody of SD14. BM is a POS who lives in the same town and maybe sees her daughter 3 or 4 times a year. The reason that ended their marriage was truly APPALLING (but that’s a story for another day).

My SO is the man of my dreams. He’s wonderful! Our relationship is wonderful! The only thing we ever fight about is SD14. When we first met, I not only fell in love with SO, I fell in love with her too. She was this funny, adorable, thoughtful girl. It wasn’t until SO and I had been together for a while that I began to realize that SO didn’t make her do anything she didn’t want to do. At 14 she should be being taught to be responsible for her own things, belongings, homework, pet, chores, etc. I was nervous before moving in, but thought it would be ok. I guess I figured there would be more compromise between the two lifestyles. I’m in no way a strict parent, but my DS is responsible for his own things and picks up after himself, etc. SD leaves everything she has, wherever she sees fit in dropping it. And unless I pick it up, it will stay there for all eternity. DS has chores. SD has none.
She is wasteful, which is a big pet peeve of mine, and she has no concept in the value of a dollar.

When DS and I moved in to their house, things began changing. Partly because I expect certain things out of my son and I guess I was silly to expect certain things from her as well. If I reminded her to pick up after herself, she would roll her eyes or give me a nasty attitude. I spent a long time ignoring it. I didn’t say anything to her, or SO. I should also mention that SD is severely ADHD and not medicated. She has obvious emotional issues because of what her mother did to the family. She has no friends at all. Her older sister doesn’t like to spend time with her because she is so hyper. So really the only people she has to “hang out with” is her grandmother and her father. When her sister wont hang out with her, she manipulates SO into doing something with her to make her feel better (And that’s not my interpretation. I heard that from her own grandmother). I have had several conversations with SO about needing more alone time (because SD is quite literally always around. She bursts into our room without knocking and actually walked in on us being intimate once.). A once a month date night… something! He usually tells me that he agrees and we do need more alone time, BUT SD has no one else and he can’t leave her with her grandmother because she isn’t in great health and her grandfather doesn’t want her around. We have also had conversations about her attitude and I have been told that I have an attitude in return (Hell yeah I do! Duh!) and also that SD hates being corrected and “that’s just how she is” and if I need to correct her, I should come to him and have him do it (tried that, but he usually doesn’t do it).

So after months of arguing and fighting and things getting worse and worse, things came to a head yesterday. I began packing to leave after I was told that I was “mean to her”, something I have NEVER in my life been accused of. When I confronted her and asked if she really thought I was mean to her, she proceeded to tell me that “knitpicking” at her about picking up after herself, and having a relationship with her sister (because she doesn’t) were rude and mean. The biggest, scariest thing in all this is that I honestly felt like she was enjoying it. She told me I brought this on myself. And after she told a complete and total lie to SO about our conversation, I asked her to clear it up because my character was being assassinated and her response was “Do u want me to feel sorry for u??” I have to wonder what other “misunderstood words” she has told SO or her Grandmother about me. How many lies has she told? Because Grandmother and I don’t have the same wonderful relationship we used to. SD is incredibly sheltered and naïve and gets completely offended when SO or I curse. However, yesterday when she stood up to me and told me how she felt, she cursed several times. I have also heard stories of when she was a little girl and her sister wouldn’t play with her, she slammed herself up against a wall and began screaming. When the parents came running, she said that her sister had shoved her against a wall. (When a 7yr old child starts behavior like this, I can’t imagine them never doing it again.) She told me yesterday that I would not get “alone time” with her Daddy because she has no one else and that I was “just jealous of and Daddy”.

SO thinks SD can do no wrong. He feels sorry for her because no one wants her around. I understand feeling the need to be on your childs side. But after yesterday I watched her enjoy the confrontation with me and realized, she wants me out! I think I am threatening her “place” as her Daddy’s BFF and making it difficult for her to do everything with only him. SD20 has told me that this is her MO. That she has done this before and has done this to her (SD20) her entire life. SO treats SD20 differently than SD14 because he feels sorry for her and acts as if she can do no wrong.

So, what do I do? I have come to the realization that no matter how great my relationship with SO is, if she wants me out, she’s gonna work her ass off (for a change) until I’m gone. At this point, I’m trying desperately not to hate (or punch her in the face) because I know this is probably all a manifestation of being abandonded by her BM and maybe a little bit of Oedipus complex. But I also feel that her behavior is somewhat sociopathic. I don’t know how to move on or act normal now and if I try talking to SO about her, it will not end well. I really don’t want my relationship to end, but I don’t know what else to do at this point. I have started taking anxiety meds because of all this. HELP!