I think oneitis is just the result of you longing for the frame you once had.

After a period of disprespect, cheating and beta simping, i was dumped.

After that ensued a period of drug addiction, depression, and humiliating myself messaging her.

Oneitis is the mourning of ones lost SMV.

Cure:

In economics, there is a fallacy called sunk cost fallacy.

You cant get back what you have lost, but you can make more money (gains) in future. The cure is to start again from scratch, as a child you fell over countless times before you could run.