Cast Darkvision and explore the right branch

After walking half an hour inside the mountain, you smell the molten metal and smoldering embers, the place is more like a temple carved in the mountain instead of a cavern. There is light in the next chamber, the big glow of a dragon’s hoard. A huge dragon rests over his mountain of gold, looks at you and smiles.

"Ah, a new servant, how... convenient."
He moves a collar made of iron with his mind and order you "Put it and take off you clothes"

What?? this creature is insane or what the hell is happening here?

He notices that you are doubting and says "You will serve me, tend my hoard, warm my lair, and obey my commands and of course, serve me as my sexual pet with my other male human pet. I need a girl too, you will be fine..."
He exhales a cloud of black smoke and says.
"Displease me, and I will sacrifice you to the mountain gods"