I recently learned that your brain loves to follow patterns, whether it be psychical, emotional, or whatever.

So thinking about a girl and her amazing traits for a period of time develops a pattern in your brain. This is how oneitis sets in. Your brain can't help but flip to this default pattern where you think about this girl and how she is the one upon receiving a cue which activates these patterns (whatever that may be)

If you realize this is simply a pattern your brain is following, it becomes much easier to shrug off oneitis. Just substitute what you usually feel when you think about this girl for a new thought, such as about how awesome you are. Hopefully a new pattern will be built in.

Thanks to this, things are a lot easier. I still have oneitis, but its not crippling. Its just a minor and occasionally annoying thing. I believe soon enough it will fade out.