See, when they become "couples" it kills the show. All shows. They are always better when it's just sexual tension.
If Clark and Lana or Clark and Chloe ever become a couple they must immediatly kill Lana/Chloe or end the show. Otherwise the show will just die terribly.
Friends went down hill when Ross and Rachel hooked up.
The creek went down hill when Joey and Dawson finally hooked up.
90210 started it's slow descent when Brenda and Dylan became a couple.
Think about all the great dramas..... when the key couple ends up together, the show loses what made it great.