My live-in partner (although our relationship is currently on hiatus) is going through another period of major detachment and I'm not entirely sure some of his current uncharacteristic behavior right now doesn't add up to an alter he doesn't know about.

If it is an alter this one seems to be a teenager. For one thing he keeps stealing my car and is resistant to me trying to establish reasonable rules around car sharing. He is thirty two and going to raves, doing stupid drugs, etc.

As far as I can tell from his trauma timeline this age in his life would have been just after most of the terrible things had stopped but when he probably would have felt most abandoned by parental figures who should have protected him.

Trying to communicate is, well, like trying to communicate with a freaked out, shut down teenager. Also most of his alters tend to serve a purpose one way or another and don't stick around long. He seems to be digging himself in a hole and I cannot get through to him at all. Any advice?