I'd have to go with this, it would be a way to seperate your time thinking of WoW characters and sexy time with your girlfriend.
I'm curious as to how you didn't come accross porn to be honest, but I guess thats another story. I assume you must have knew about it at some point during the time where you "had no life".
Anyway back to the point - Since you feel weird while your lovemaking, you need to realise that it will effect the way you treat her, I'm not talking in the mechanical sense, but in how you feel. You will come accross slightly awkward or held back to her if you have had "normal" lovemaking for a while before you started thinking about it again. I think what Gandrake suggested is actually good advice, as odd as it sounds.
But yeah. Don't tell her. Don't even hint at it. Its not lying, I believe it's something you'll get over with time, try experimenting with sex more to engage you, specifically more face-to-face positions; you cant help but look at her and just enjoy the moment for what it actually is then. The honeymoon period is the best anyway.
As long as she can take your mind off it before sex and keeps your mind off it during, it should be more enjoyable for both parties.
It may take some, uh, "social engineering" to get her to change how she comes accross during sexytime though.
But hey, maybe I'm just missing the point.