There comes a time in each person's life (or so I believe) when they come to a sad realisation...
You have always been friends but lately not as close as before. Things start changing and you start to notice interesting behaviours. You are no longer included in their plans and they (or so they think) are not included in yours.
Things that were cool before now cause quarrels and conflict (generally one sided); accusations are thrown about (again usually one sided) and lots of confusion ensues.
One sided demands/requests are made often under the guise of "well I wouldn't do that to you", however the reciprocal demands/requests cannot be made. They will expect and ask of you that which they themselves do not, will not, and possibly cannot give.
Things, actions, words will be taken personally despite a million and one assurances that it wasn't personal. The culture of "it's about me" and "why did you do that to me" becomes very pervasive.
Something that used to give you joy now just leaves you feeling empty, used, and to some extent alone. You have invested a lot and realistically gotten nothing in return.
There comes a time in each person's life (or so I believe) when they come to a sad realisation... that they are just a side piece and/or security blanket.