I saw this being mentioned in another post, and there seemed to be some misunderstanding.

Firstly, what is it: Oneitis is an intense, unhealthy romantic obsession or fixation on a single person—often treating them as "the one" or a singular source of happiness, usually to the exclusion of other partners, realistic perspectives, and personal well-being (from wikihow).

What des this actually mean in layman talk: You see a girl/woman and you obsess over them.... In your head you are playing some movie involving you and them. You spend a lot of mental energy letting them live rent free in your head.

Maybe they are someone you see in passing, maybe they are a "friend".

What you do NOT do however, is let them know how feel about them, ask them out, make a move, etc. Its all just going on in your head.

To make things worst, their may be actual women interested in you, but you would rather live in your fantasy (that you never try and make reality), so you ignore everything going on in real life. To make matters worst, this can affect other areas of life due to your obsession.

What it is NOT : Actually dating someone is not Oneitis.... interacting with someone and setting up dates is not Oneitis.

Cannot find the exact post, but someone claimed that being exclusive with someone was Oneitis.

How to cure OneItIs:

Make your interest known (better than friendzoning yourself)

Go sleep with someone else, and see if the obsession remains.