In other words, get over yourself and your obsession with that girl, because it's just an illusion. And when you get rejected, don't be depressed. Because there's really not much to worry about.
Normally, a person does not get over oneitis until they are fairly sexually and romantically experienced with several partners - that is because at that point a person may realize they are not that different from each other, the romantic victims, and that each of them was not special and unique, and if one is to seduce their romantic victims and have their romantic victim in thier hands they must not develop oneitis. In other words, oneitis is often overcome with experience and practice - that is what a seducer must accomplish if they are to truly be a master of their craft.
Some helpful advice for getting over oneitis during a seduction is never stop flirting with other members of the opposite sex, never close yourself off, never say that this is the one. Never stop meeting members of the opposite sex and so on.
After a seduction is over and you are now broken up you may develop oneitis thinking that that was the one. You can get over that by meeting new members of the opposite sex, flirting with new membersm, meeting and entertaining them.
THe general advice for getting over oneitis commonly heard is to meet up to ten members of the opposite sex, seduce each one and have sex with each one as soon as you can, one after the other. I do not recommend going that far it does not take that much, it is forwned upon because it is cheating, and because oneitis can affect a male or a female seducer at any point in a seduction.
Oneitis has it's origins as a word and a concept in the seduction community, where it was first discovered and analyzed by accomplished and acclaimed seducers.
Common symptoms of stage 1 ONE-ITIS are the following:
-thinking she's so much different from any other girl you've ever met.
-thinking she is the most beautiful girl in the world.
-thinking she is to at least some degree innocent and moral. (See definition of a slu.)
Common symptoms of stage 2 ONE-ITIS are the following:
-calling her 2-3x a day, just to talk.
-staying on the phone when she calls you.
-analyzing everything she says and does. Example: "I saw Mary-Slu in the hall today, she looked my way, what did she mean by that???"
-completely ignoring every other girl who shows interest in you.
-asking anyone and everyone for advice and to over-analyze her actions.
-thinking your different from the other 100000000 million "good guy friends" she has. Reality check dbag, YOUR NOT.
There is only one simple explanation for the term: An unhealthy romantic obsession or fixation for/on one person. This mental disease will often interfere with your ability to attract said person, due to your clingyness.