I agree with you 100%, if you have hardcore oneitis, it's hard to find another girl that "measures up" to your oneitis just because you built her up so much in your head. If you take your mind off girls completely, you can get over her. I find that's what works. Do an activity that takes your attention. I'm rebuilding a Volkswagen drivetrain for an old beetle, and it has taken my mind completely off an old oneitis. I don't even talk to the oneitis anymore and I doubt I ever will again. I haven't spoken to her since last Wednesday, and that was just her contacting me because she was too busy to talk, but she wanted to see how I was doing....? So I doubt I will be hearing from her again, because I have stopped contacting her.
