The 'logic' behind the thought process is as follows:
If someone extremely special to me treats another person or persons as special, then I am no longer special to them.
It is based on my assessment that the 'special' status is only applicable if unique, roughly in line with the definition of the term.
As such, I cannot accept that I am special to aforementioned someone, if someone else also shares that status; or I perceive them to also receive the status.
This often manifests as;
If this someone has other friends they like a lot, they don't like me because I am no longer special to them.
This conclusion results in extreme jealousy, rejection anxiety and anger - towards both the person and their other friends.
The extent of the emotional responses to anything I perceive as compliant with the above assessment is extreme. It is overwhelming and I am completely at its mercy.
This is destroying my friendship with someone who is extremely special and important to me. I believe it is a flawed mentality, yet I remain powerless to overcome it.
That is my predicament.