You decide to stay with them, there is nothing too important in your world waiting for you, but this... It's a unique opportunity.
And... if it's bad, you can just use the stone and return to your world.

The dragon’s lair becomes your kingdom, his hoard is now your hoard. The devil-woman teaches you her secret arts of pleasure with hands, mouth, pussy, ass, and other parts of your body. The dragon watches and also uses his ancient secrets to please you both...

He delights in your shared marriage.
The stone is forgotten on the bedside altar...

You play kinky games together, using shackles, collars, and other artifacts. After many years, you always find a way to try new things.

You have a happy life together, full of lust, desire, and love... even when he says that wants a third wife you laugh and your eyes glow with expectation.

THE END
Happy Ending: Dragon's new wife

Task: Wear handcuffs and a collar with a leash, caress your nipples and main hole using rubber gloves, and imagine the devil-woman playing with you. Act aroused and moan. Masturbate for 3 minutes, do it slowly, and don't cum. Prepare a well-lubed huge dildo and slowly insert it. Fuck your hole gently for 5 minutes, move your hips, and control the rhythm, cum moaning like a whore. Hug 2 pillows on the bed and imagine your new happy life.