Hi @Jossy,
As you say he doesn’t have papers yet, I presume he has the paper called ‘Aufenthaltsgestattung’. With this paper he is not permitted to leave Germany. If he wishes to go and live with you in the Netherlands, then he would have to revoke his asylum application first. He would then probably have to apply for a visa at the Dutch embassy in order to travel to the Netherland to sign into a partnership with you.
Best,
Éanna