Cupid is sadistic. The little winged guy with the quiver of arrows and lack of diaper loves to match thermostat crankers with thermostat killers. Opposites attract, but always under the optimistically silly notion that they can reform the faults of the other person. Consider my friends Tom and Denise, perhaps the most drastic case of mismatched degrees I know. Here she comes, mummy-wrapped in layers of afghans, nudging the thermostat north with her frozen nose. That’s him a couple minutes later, strolling by in gym shorts, sweat dripping from his brow, as he knocks the numbers back down. Sure, they love each other. They’d just rather do so from separate climates. Similar dramas are playing out in households all across the chill zone as mismatched pairs try to survive each other. ‘‘What,’’ each person wonders, ‘‘attracted me to this wacko in first place?’’ It’s simple: Opposites attract. Or so the claim goes.