>call me out on being on denial
>taking tv tropes source as legit proof
There is no proof it was a on the lips. There is neither proof it was on the cheek. As I said above it could be any as didn't get to see it. It was stated in an interview that in the script of that episode they didn't specify where did Serena kiss him and that it was up to the viewers' imagination. If not shown we have no idea where did she kiss him, it could have even been a forehead kiss. As I said, it could be lips, cheek forehead or whatever you like, it's up to your interpretation.
My bad. I misrecalled. I re-read the interview and they confirmed it was a kiss on the lips. Don't mind what I stated above.