Horrible Night, Great Neglection

[SORT OF DRUNK MESSAGE] *apologize for the crude writing*

Instead of carelessly texting people of my feelings, I come here tonight(or early morning) feeling the most neglected, the most inefficient, and the most unappreciated person without knowing who would be reading this and understanding. you know it always comes down to people I always cherish. The ones that I can say that are special and loved from the capacity of what I have left of love that I can afford to give, that are the ones that breaks my heart the hardest. Tonight after a couple weeks, I went out to the usual weekend spot, to see a dear friend, or at least a person "I" call a dear friend to me. I could've stayed home, could've just spent my night relaxing with a movie, tv show or even playing Final Fantasy 14, but instead I brought myself to go out after awhile, just so I can be with people that I can drink with, and physically be around with, but instead I come home wondering and evaluating the certainty of the friendship I have with them. Now I know that friendships shouldn't be usually evaluated but instead trusted with faith.
After a couple nights of this....neglect, tonight I realize that I'm no longer a person people consider a friend, or close friend. Maybe a friend when its convenient or without other options, but I can tell that I will always come second or last place. Even from past relationships I realize that I can never compete or be better than others. I swear I timed her of when she would notice me and take care of me, but she just kept being with others. I wasn't served for almost an hour, and its not about the service as a customer but the base principle of being a friend as she said that I was, would get some sort of attention, but tonight all I got from her were just a few drinks and drunken hello and some venting.
There were other customers that was with her of course, and mind you that I understand when a person gets busy at work then they are busy, so there is no reason that I wouldn't understand. But she wasn't, and I've known her longer than the others, and tonight as the third time(even though it has happened plenty of times before) I've been ever so neglected and actually came home sort of sober and straight. I seriously didn't get any attention but instead Barbie and others found a way to keep me from breaking down again tonight.

I ask this question; So if we've known each other for so long, and proven each other of the friendship that has been built ever so well after so many years, what makes one person so easily neglect that friendship?