DS who is trying to recover got an absolutely abusive text from his other sister saying that if he does not go and she dies that it's his fault.
She posted on Facebook but never contacted her brother. He found out by waking up to messages from people who saw the post.
You're describing what sick people do, but as upsetting as it is, there's really nothing you can do about it. Often times the best play is to do nothing, and the benefit of this is the person acting out attracts a lot of negative attention they don't necessarily want.
Do your best to keep your focus on you, and your boyfriend. He's going to need your support in the hours and days to come.