Believe it or not, I was asked out by 2 other women who were better looking than the object of my affection... but I couldn't see past my own blind desire for this one woman who wouldn't give me a straight answer.. yes or no. She didn't want to hurt my feelings, and yet she would unintentionally stomp on my heart every time she talked to another guy, and gave out her phone number... right in front of me.
The reason I'm admitting this "less than pretty" part of my past is that I want you to know that I understand what it's like to be so focused on getting the approval and winning the affection of one single woman... that you ignore all other perfectly good opportunities.

I think there's a little bit of one (or all) of the above mentioned guys in each of us.

The good news is that you can easily break past the limitation of oneitis. All it takes is making some simple distinctions.
By the way, I'm not saying that you should date multiple women forever. My own personal philosophy is that you should
date 2-4 women at once and then narrow it down until you find one great girl that you want to have a relationship with.

I've done this myself. At one point, I was dating (and sleeping with) 5 different women. It got to be extremely confusing and difficult to keep track of each one's needs and schedules. Luckily, out of those 5... one emerged as OBVIOUSLY better for me than the other 4 women.

That's not to say that she was a better human being. I'm just saying that she was much more "right" for me, than the others were.