Because this socially inept nerd has never had any other interaction with another "female". He is so wrapped up in these Freudian-esque feelings for someone he has become so close to, he hasn't even allowed himself the possibility of getting close to anyone else.
Who else would hold up to her standards? Who else would be as perfect as this pedestal-lifted goddess his mind has created?
This dork just wrote a 1400 word essay that could be summed up in 60 with a well placed run on sentence:
I'm a loser, I'm fat, I'm pining over a girl who is obviously too good for me, and since she is the only chick I've ever had the balls to talk to, and who was kind enough to actually give me some attention, I am, of course, going to risk it all and try to make a move on her.
You want some advice? Lose the 80 lbs., the acne, the social awkwardness, the chick "best friends", the pathetic obsessions, and stop thinking everything is a "sign" when it isn't.
Translation for the slow - She's boning some other dude who is getting the job done, and you are the backup plan / shoulder to cry on. You will never successfully be out of this position, so do yourself - and the rest of us - a favor by accepting this, and moving on. It's obvious she has.
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