Tell him you can't sleep over because...his pillow gives you a stiff neck...you cat gets lonesome...you're allergic to his bathroom tile. Even if his place is more of a hovel than a home, he'll probably prefer that you spend the night on his turf - where he feels comfortable. But constantly consenting to do that is a mistake, because it gives him all the power. About half the time, you should say you'd rather stay home. Alone. Soon, he'll be aching to spend the night in your bed! We he does, make him feel welcome: Stock his favorite CDs, keep a beer mug chilled in the freezer, give him a smidgen of room in your closet for business suits.