"Unfriend"

"Make new friends but keep the old.  One is silver and one is gold."

I have never before found myself in a situation where I needed to consider breaking off a friendship with a friend; let alone such a close friend.  I have always had an interest only in repairing damaged relationships and doing my best to mend the frayed edges.

However, when one is convinced that my best attempts (considering current circumstances) aren't enough for our friendship, what is left for me to say or do?  Am I expected to stand by and continue to defend myself against false accusations which are based on one's seemingly twisted perception of reality?  Continue to make plans knowing that she will either show up late or not show up at all?

• I don't receive any respect in return for the respect that I give.  Showing up late with no apologies or concern for my time, frequently canceling on plans or being very noncommital ("maybe I'll stop by" or "maybe; we'll see") even after confirming "definite" plans.  GAG!  Who wants to try to make plans with someone like that?  Someone who is more interested in what they can get out of an outing rather than what both or all parties get out of the experience.  Someone who seems to have no respect for the time, tight scheduling, or interests of other people.
• She appears to be self-absorbed, shows little interest in my life, and is constantly creating or being surrounded by drama that just wears me down and leaves me feeling exhausted when I'm done hearing all about it.
• When we do go out, I always feel as though she is never really focused on our conversations or what we're doing, but rather more focused what people around us might be thinking about her looks, what she is saying, or what she is doing.
• My honest opinions/advice are usually very quickly disregarded while I am expected to be all ears for this friend's opinions/advice because this friend is "always right."
• I am always having to justify my actions or lack of actions.  When perceived misdemeanors are accusingly brought to my attention, my explanations for the falsely accused wrongs never seem to be good enough to quell her mistrust. 
• I seldom feel comfortable expressing my opinions with her because my opinions are usually never taken seriously or acknowledged, unless such opinions make her feel good about herself.
• She blames me for not making enough time for her even when I have multiple commitments involving family and work.

The value that our friendship has to me does not change regardless of how many weeks we may go without having a chance to see each other or how many important life details we have to catch each other up on after those few weeks of separation; I understand and respect her schedule as well as my own; I expect to be able to pick up where we left off and have no judgements placed on each other's choice of scheduling.  But it seems to be that the value she places on the friendship fluctuates readily in the face of any doubtful thoughts that cross her mind.

My automatic response would be to salvage the friendship and soothe any hurt feelings on her end that are due to many misconceptions that she has.  But I'm questioning whether the respect, interest, consideration, patience, and understanding are going to continue to just be one-sided?