You have generally used the term desire to cover every motivation for will, or purposive action. This is too broad in that it conflates too many heterogeneous elements. This conflation smacks somewhat of Buddhism and brings with it a certain negative connotation. If you wish to examine the phenomenon clearly and without judgment the term ought to be confined to sexual desire. Thus, proceeding, an existential account of desire takes it as arising out of a certain way in which intersubjective reality is apprehended, or better, lived-out. In contrast accounts in the spirit of psychology and especially psychoanalysis which are less interested in how it is experienced and more in how it is occasioned, treat desire as resulting from certain kinds of scenarios. For scenic theories of desire, and this includes theories of mimetic desire - aren't they all mimetic in essence - as well as evolutionary accounts, desire is always fictional, illusory, and in essence perverse (but not the perversion of any thing). Paraphilias are paradigmatic, and there is no essential difference between scenes of desire played out in real life and those represented in cinema. If you could speak of existential desire in contrast to psychoanalytic then you could say that in the former the truth of desire is to be found in desire while for the latter it is in the understanding of its essential untruth. The latter view has been so much in the ascendancy in recent decades, that you need to fight your way to a grasp of the simple evidence of the former, even when it is right before your eyes.