Reading your last few updates and the actual text message - I have a really spooky feeling of familiarity. My older DSD has targeted me, (her step mum) similarly but now her boyfriend’s Mother. She’s not as extreme, but if I explain a little of what I’ve learned about her, perhaps... who knows, it might help with your situation?
It actually gives me shivers reading how this girl is targeting you. It will not stop, and will always be there. She’s shot you a ‘warning’ and she’s won. She’s kept her BF, your DS, despite saying awful things about you.
My DSD is a very intense girl, very awkward and at first seems shy and sweet. However over the years, I can say this on mumsnet, (but would hesitate in RL), there is just something wrong with her. She has an underlying aggression that simmers, always, I don’t know why but it’s there. She latches onto to a man and sees their family as competition and the enemy. Her current BF has serious mental health problems and went back to live with his mother. DSD, I honestly don’t know if she controls her BF the way your DS is being controlled, but she is incredibly immature and I know depended on a BF and he could not cope with her pressure.
DSD saved a lot of money and tried to get them a flat away from his mother. She told her BF her mother was suffocating and controlling him, said horrible things, demeaned her, really targeted her. His mother stood firm and according to DSD ‘didn’t allow’ her DS (19) to move in with her, which made DSD enraged and furious. Something tells me that mother is protecting her son and from the outside, I’m glad she has as moving in would have been a disaster. DSD was talking babies.
For DSDs sake I am also really glad that her BF didn’t move in with her. Whatever provokes this intensity in her to be all in on a BF and nothing else in her life, and to hate anyone who gets in her way, I think if she did cause her BF to get worse mentally, she’d feel devastated. I sometimes think she might one day hurt herself, or retaliate against some imagined slight, in a devastating way. I fear it and it wouldn’t surprise me. Someone has to put the brakes on her intensity for her as I don’t think she can do it herself.
DSD’s parents (I’m now separated from her Dad) do know she’s ‘difficult’, her mother couldn’t cope. But they did try their best, but in no way see how she can target people in a way that she did me in the past, and now has again, who would want to think that of their daughter I guess? DSDs parents were relieved when she got a BF who seemed decent and as they saw no issue, supported them to be together. To be honest her mother wanted her out of the house again.
Sorry I don’t know if that makes any kind of sense or is helpful in any way. But the targeting of a mother is similar. I don’t think your DS or his GF have the maturity or capacity to rein themselves in.