Hey there

I am here because the 15 year old son of my partner, is causing some difficult situations. And I am at loss about how to handle it.
His mother and father are divorced for 13 years now, so he has two homes.

He is causing some difficulties by manipulating both homes (us). Whenever he is not getting his way in one home, he 'flees' to the other, tells a sad story and then gets his way.
Whenever he misbehaves or does something that is not ok, he purposefully causes a big fight over it, so that he can flee to the other house again, and tell the sad stories.

At first we just send him back, after talking about it with a cup of tea. But his stories about his mother have grown really horrible, and its difficult to see what is true, and what is not. Its difficult to send him back when you do not know for sure that all is ok.
I suspect that a lot of it is not true, but when you do not know for sure.. you cannot do anything else than try to protect him.

He knows this, and he uses it willingly.

The other way around he does the same. He lives with us now, but whenever he has trouble because he did something, he suddenly wants to sleep there.

The mother does not talk to us, never has, and the lack of communication comes in handy for him. He can freely choose what to tell us, and we have no way to check if it is true.

How should we handle this?
When we try to talk to him about it he ignores us or starts shouting, which is something he does to scare people away. So that they do not confront him.

I am so at loss about all of this
He is a good kid, but this is not helping him to grow into a healthy adult at all. I do not know how to change it.

Another aspect of the situation is that I am chronically ill, I have POTS. I have a 'serious' lack of energy. He is aware of it, and also uses that. He knows that when I am tired, he can get away with more.
Physically I am sometimes unable to address that.

I know I make him sound like a horrible kid now, but truly he is not. In nature he is really friendly and the enthusiastic type that makes people laugh a lot. But the divorce/two homes situation has given him too much power, I guess he is used to it now.
If communication with his mother was possible that would help a lot, but its not, so thats a road that is not open to us.