The seven stages of grief are shock/disbelief, denial, anger, bargaining, depression, guilt and acceptance. Harry Potter is a story reflective of the stages of multiple facets of grief with the story arc resolving in the perseverance of hope, the everlasting nature of love and each character representing emotions within each stage of grief. Even the seven books composing the series represent the various stages of grief; each book's overall theme crystallizing an element of grief. Needless to say, spoilers ahead.
The story begins with shock or disbelief in the murder of Harry's parents at the hands of Voldemort. The shock is shared by the viewer/reader, Harry and (we later learn) Snape. The grief is not necessarily over the loss of life, but more accurately, the loss of love. Conversely, the seeming destruction of Voldemort, while significant, is not a matter over which grief is evoked. His destruction is a matter to rejoice over.
Character emotive identity
It is worth recognizing that Lily Potter and Severus Snape are the personification of love. Lily represents the loved; the ideal. Snape represents unrequited love, manifested in heartbreak. They have the same patronus, because a doe is symbolic of love. Dumbledore recognizes this in the afterlife, when he responded to Harry's inquiry about it being curious; it doesn't seem curious at all that they have the same patronus. They are two sides of the same coin.
James Potter is a less significant character in the story arc because he represents ambition and pride. His character is more of a warning, a marker of the perils of easy triumph. He was the proverbial jock, the mischief maker, the popular youth who acted before thinking and had a bit of a bully streak. We know snippets about him, his interaction with Lily, Snape and Harry. One wonders why James Potter didn't immediately take his family far away from Voldemort's reach and protect them from harm. Was pride his undoing? Snape, in the aftermath, took the hard path and acted out of unselfish love, as shown in his silent aide of Harry through the series. You are left to question - who really was the better father figure to Harry? Who taught him strength? Would he have had the courage to face his fate, but for the knowledge, Snape's last memories showed him? Snape was, after all, "the bravest man" Harry ever knew.
Snape did not protect Harry, because he was James' son or even because he was the "chosen one". He did it because he was part Lily and his love for her survived her death. Separate from any cruelty James inflicted upon him, part of Snape's resentment for James was because, in his mind, James was the direct barrier between he and the loved (Lily). In his mind, had it not been for James' pride, Lily could have lived. The underlying psychological reason Snape cannot help, but treat Harry with an unkind disposition, is because Harry is a walking, talking reminder of the loss of Lily and Harry also shared some of his father's traits, which Snape remembers in the context of the cruel treatment he endured. In Snape's eyes, Harry is the patronus of his heartbreak and a ghostlike reminder of the pain of his youth. He is calculatingly mean as opposed to cruel. The cruel relish the suffering of others.
Voldemort is the personification of greed and the enemy of love and hope. All of the Death Eaters are facets of greed, whether they be the Malfoys representing greed in material wealth and status or the cruelty inherent in greed as represented by Bellatrix Lestrange or any others. Prior to Lily's death, Snape as a Death Eater represented the void which becomes of greed in his heartbreak and jealousy of James' union with Lily. Upon the death of his beloved Lily at the hands of Voldemort, Snape turned against greed and transformed himself into a selfless, but tortured soul.
Harry represents hope throughout the story arc and when love (Lily) sacrifices herself for hope (Harry), greed (Voldemort) tries to destroy them both, but ultimately destroys himself. Dumbledore was half right when he said that a part of Voldemort lived in Harry. A part of Lily also lived in Harry through the love with which she protected him. The Dementors were not attracted to Harry because he had a part of Voldemort in him. Dementors drain goodness and light from those they torment. Lily used love to protect Harry from death and that love stayed with Harry as a tangible part of his being. The Dementors were attracted to that like a moth to a flame. In a similar but flip side manner, Snape arriving at the Potter home, passed pride (James) in the stairwell, without affect and is devastated by the loss of love (Lily), and in that devastation, heartbreak (Snape) does not even see hope (Harry) crying right behind him. Heartbreak is in a tunnel vision of despair, but nonetheless founded in love.
Aside from greed stealing away Snape's love, Harry, with his mother's eyes, is the last remaining living part of his love and paradoxical, also the last living part of greed through his connection with Voldemort. In this regard, Harry is even more clearly defined as hope. Love and greed twisted in fate and balanced in the desire to bring about what could be. If the eyes are truly a window into the soul, then it must be said that love is the soul of hope. Several times, Snape hears that Harry has his mother's eyes, but we don't see the emotional current and impact until he looks into Harry's eyes and acknowledges it himself in his last moments. Snape inviting Harry to take his tears, is the fulfillment of his love for Lily, through the knowledge he gives Harry and the knowledge he withholds from Voldemort. In one act, Snape embraces and protects love over greed as if to have made it to the Potter home in time to save Lily.
The holcruxes represent greed's denial of its own destruction. Greed wants to be eternal. Greed most wants to be love and hope or at least their power. The division of Voldemort's soul was intended to make greed eternal. In essence, greed wanted to supplant love. That part of Voldemort's soul which latched itself on to Harry is greed's desire to steal eternity from hope.
Throughout the series, all of the characters loyal to the Potters try to help and save Harry, while Dumbledore knew all along that Harry had to die. Snape's comment that Dumbledore was raising him like a pig for slaughter, casts a justifiably blunt light on the futility of the denial.
Snape's own subconscious is a matter of denial. His unkind treatment of Harry is misplaced anger towards James. His protection of Harry is an homage to Lily. In this regard, instead of Snape treating Harry as he would any other student, he treats Harry as a surrogate for the conflicting feelings he had for the Potters.
Throughout the series, Voldemort's blind anger and cruelty in killing everyone in his path to immortality is his ironic rebellion against death. His demeanor, even towards those loyal to him, is wholly founded upon the anger which is attendant to greed. One is angry in greed because no matter what is gained, the greedy always want more and are enraged to not yet have it. Voldemort was in a rage to know the prophesy of the one who would end him, Harry.
Harry and Snape become increasingly angry as each story progresses. Harry becomes angrier, because he becomes more desperate to avoid the fate of dying. He becomes more clearheaded about what he must do and less patient to explain the reasons why he must do what he must do to his friends. Snape becomes angrier and angrier also because his ruse is harder and harder to maintain and he must continue to do increasingly unpalatable things to further the subterfuge.
Throughout the story, there are bargains to avert or circumvent fate. Voldemort bargains with death through extortive means. He simply wants to trick death and live forever. He used the horcruxes to cheat death of taking him. Snape bargained with Dumbledore to try to save Lily from death even if it meant saving James, who he despised. Harry's bargaining is with time, more so than anything else. He tries to race against time to destroy the holcruxes to be able to defeat Voldemort, but it is futile because he too is a holcrux.
Voldemort has no guilt, evil revels in the accomplishment of darkness. Snape was apparently guilt ridden for not being able to arrive at the Potter residence in time to save Lily. He was guilty to kill Dumbledore, guilty in furthering Voldemort's agenda and guilty to have played the role of betrayer, but as we learn, all of his actions were part of a plan to aid Harry. Harry was guilt ridden for all of the people who died in following him throughout the series.
Voldemort knows no joy. Even when he is smiling or laughing, it is cruelty shining through, as though the satisfaction of evil. His depression began when he was a child and met Dumbledore. And revels in trying to overcome prophesy. He becomes more and more depressed as each holcrux is destroyed. Harry likewise matures and becomes more and more depressed as his connection to Voldemort becomes more pronounced and more of his allies perish. Snape's depression is constant from the moment he finds Lily dead to his own death.
Acceptance and Hope
Voldemort has a false sense of hope and acceptance in that he believes he has killed Harry Potter for good and defied both prophesy and fate. He revels in the proclamation of Harry being dead and parading his body as a trophy. Harry, accepted his fate and did not fight death. Notwithstanding, Harry, using the resurrection stone most clearly personifies hope in escaping death not once, but twice. His survival means that Lily lives and Snape was successful. The ultimate message of the story from beginning to conclusion is that love conquers all,.... always.