My wife was the school hottie, and I was completely surprised when I asked her out for the first time and came to find out, she said "sure". We've been together ever since, I asked her once how I got so lucky, and she told me that she hardly ever went out because guys always thought that she was so good looking that she must be taken. So don't ask, don't worry about why she's single, just enjoy the fact that she likes you enough to go out with again. You start asking, YOU'LL start coming up with reasons why she shouldn't be with you.