[quote Thermopylae]@workworkworkugh, I have a teenage son myself, and I feel for you and your whole family caught up in this incredibly difficult situation. Unfortunately I also have personal experience of abusive relationships, coercive control and toxic family dynamics. Please don't think that you should have known instinctively how to handle your DS's situation right from the start. People like your DS's GF and her mother operate according to a completely different set of rules, and unless you've come across people like this before, it's easy to remain unaware that a different rule-book even exists! In many ways it's like dealing with an alien species - all the normal expectations of behaviour and social interaction go out the window.
You've already had excellent advice from other posters to "grey rock" as much as possible. I would strongly suggest that you do not respond at all to the implied accusation that your DS was kicked out of home, however much the injustice of that stings. You can't reason irrational people out of a fantasy they have a vested interest in maintaining. The minute you try to defend yourself, you give the GF and her mother the oxygen of credibility - their accusation and your response become two sides with equal weight in an argument. If you don't respond, their accusation just dangles in the air like the piece of batshit gaslighting it really is.
I agree with previous posters that keeping a line of communication open with your DS is important, but I think any attempt to establish a two-way dialogue with him - even asking innocuous questions like what his plans are for the day - will be misrepresented by his GF as an attempt by you to exert parental control. With this in mind, I suggest you keep your communication one-way - text him mundane bits of news about family or friends every few days, or send him links to Youtube videos etc he might enjoy. In other words, keep the communication channel open without demanding anything in return from him - not because it isn't reasonable for you to expect a response from your own son, but because any expectation will be twisted by GF (and her mother) to appear unreasonable.
You might find the book "Toxic In-Laws" by Susan Forward helpful for providing some insight into your DS's behaviour as well as that of his GF and her parents.
To the posters who are so keen to point the finger at the OP's DS - stop victim-blaming. This is an adolescent caught up in an abusive relationship. You've only got to read the Relationships section of MN to realise that some grown adults take years to finally free themselves, mentally and physically, from abusive relationships like this one (and some never manage it at all). Along the way, plenty of adults in abusive relationships ignore help, don't listen to advice, fall out with family and friends over their abusive partner. Why on earth should we expect someone who isn't even legally an adult yet to handle this situation any better? This young man is acting out with his parents because he's overwhelmed and petrified, and his parents are safe targets - they don't threaten to self-harm if he gets angry or upset or disagrees with them. I can only assume the posters eager to vilify the OP's DS have never been on the receiving end of abusive behaviour themselves - try having some compassion for people who haven't been so fortunate.[/quote]
I agree with all of this too.
And I also agree that the messages to your son shouldn't be daily - too overwhelming - but regular, maybe every 2-3 days, with just "we love you and this happened at home/with your siblings" - no pressure.
I particularly agree that your son is behaving like this because he's under so much pressure from this girl. He doesn't have the maturity to deal with it any better, and doesn't know what to do with himself, so is taking it out on you because he knows you will still love him whatever. EVEN THOUGH he's accusing you of all sorts, he still knows you love him.
Hang on in there - ignore the mother entirely now - and hopefully this will burn itself out and you'll have him home again soon.