Boyfriends sister is a monster!

I need some advice on how to handle this. My boyfriend and I have been dating for 3 years now. His sister came back into his life after spending 10 years estranged over money their mother had when she passed. It was an ugly legal battle which broke them apart. She came back into his life at the same time he and I started dating. I could always sense that she didn’t like me. But she would put on her fake act and we would pretend for my boyfriends sake. My previous post on here goes into further detail on her mental issues. She is literally obsessed with my boyfriend. She wants him all to herself and because she does not want to marry anyone she expects him to “marry her” in a non sexual way. That’s what she says. I find that disturbing! Anyway, couple of months ago she went completely insane and began attacking me and said some really horrible things. Things that only a jealous lover would say to another woman trying to steal her man. My boyfriend does not see her obsession with him as weird. He says they were always close up until their mother died and the money battle began. He does agree though that she is not right in the head and has cut her off completely after she called him stupid and brainwashed by me. She ended up losing her job and is unraveling every day more and more. So, my boyfriend is now getting concerned for her and wants to talk to her so she can get professional help. He and I both think she needs medication and counselling. I know his sister will never agree to it. She is very sure that she is perfect and everyone else needs fixing. She will never apologize for anything. She says there is no reason to apologize because she never does anything wrong. I do not want anything to do with his sister unless she apologizes to me and takes back all of the hurtful things she said to me. I know this will never happen. My boyfriend wants to still keep her in his life even though I want her out. He is concerned for her and worried she might kill herself. For this reason I am not forbidding him from reaching out to her. I just feel like she is doing all of this on purpose. She is no dummy and made it very clear to me that she will win in the end and get what she wants which is me out of the picture. My boyfriend and I are talking marriage and kids and moving away together. We are serious about each other. She is holding us back and doing everything in her power to get between us and try to break us up. What should I do about this? Do I just let my boyfriend go ahead and try to talk some sense to his sister and allow her to keep bashing me and trying to ruin my relationship? She will never respect me. My boyfriend says he is going to tell her she has no choice but to but I know if she agreed it would just be a lie. I want her out of the picture completely because she is not mentally right. And when I have kids, I do not trust her to be around them. She is a meth and coke user and heavy drinker. Which I’m sure only add to her mental health issues. But I do not want to upset my boyfriend and only want to be there for him and show support for his choices. Do I have a place in this? Or do I just need to sit back and allow this monster to keep trying to ruin my life because he is too nice to see through her childish antics?

What a tough situation you are in. I know how much frustration you have with this problem, as I myself would be very frustrated as well. As I was reading this though, I sort've shifted my perspective to your boyfriend. I can only imagine what a tough spot he is in. you must understand that, that is his sister that he loves and probably will always love, as the same goes for you. He loves you and doesn't want to see any of you ( You and his sister) leave. Honestly, the only way I can see that all this works out is the three of you sitting down and talking about this. Talk it out. Face to Face. No Texting, No your boyfriend only talking to her. Sit down, ask her why she's acting like this. I know in your mind your saying to yourself " I just want to get rid of her and don't give two sh*ts about her." You can obviously tell this lady needs some help, and I really think the problem is that maybe she never had someone she can really talk to and express her feelings on what is going on with her life... ( which is probably why she started doing drugs in the first place, to cope with some depression issues...) As I said with you guys having a little chat, all three of you, I really believe that if you have a heart to heart talk and give her a reason to like you, she will open up and hopefully can get some help with whatever issue she has. In conclusion, I really hope what advice I have given really works out for you, as I really believe it will work out. Not only will you cherish your relationship, but also helping someone who really needs it. After all, this poor lady could really use it, and might even end up saving her life...