Fiancé has TERRIBLE hygiene!!

I love my fiancé with so much passion. He's the best thing that has ever happened to me!
But..
He has terrible hygiene. We live together and it drives me nuts. His teeth are almost BROWN and rotting out of his damn head. He showers MAYBE once a week. He wears the same clothes for days and days without washing them. 
I'm not the only one who has noticed, either. My mom has asked me about it. My aunt is worried about him. 
His family isn't this way! His mom has a spotless house and takes great care of herself. His dad, too. Even his brother brushes his teeth. 
I brush my teeth twice a day and I ALWAYS ask him to come with me and brush his too. I'm super nice about it and I don't complain. He just won't. I don't know what to do!