Possible reasons (for why you miss her):
1) The psychology of your online life is catching up to you and you're suddenly feeling an overwhelming need for human companionship.
2) You're part of the computer generation, and therefore have Instant Gratification issues.
3) She left recently and you enjoyed her company.
4) Because your mind is reacting to some sort of counter trauma treatment she provided (some sort of 'everythings going to be OK' thing).
5) You have an interest in her and are in denial.
6) You have established some sort of symbiotic telepathic connection that becomes detrimental to your health when you are out of receiving range.
7) She took the cake, cookies, and pie with her.
hmmm....
Yep, overall it sounds like typical adolescent behavior.
That, or you have serious manifestations of schizophrenia, bipolar disorder, and de Clérambault's syndrome all occurring simultaneously.