AN JK Rowling own Harry Potter and I make no bucks, pounds pesos, etc. from this because I write for enjoyment and those who choose to read my stories.
I was watching the video from the movie and wondered what Snape was thinking after he revealed his memories just before he died. It is said one reflects on their life as you die. This is what I think happened.
He looked desperately for Potter to tell him everything and failed. Growling out in frustration he cursed. The boy he could not stand needed to know, yet no matter how much he searched during the battle he could not locate him. He pushed deeper into the battle focused on one goal. Harry Potter.
Snape found himself in a two on one battle and hexed the couple strongly watching them fall to the ground and remained there unmoving but alive.
He looked around him warily to fulfill this last act knowing that he would not live to see the sunrise of the next day. It was time for the young whelp to know that he needed to die.
Hearing a crack of Apparation he twirled around, black robes billowing from the movement and found Lucius Malfoy standing in front of him.
Lucius quickly killed two attackers with a flick of his wand and spoke urgently. "He wants you at the Shrieking Shack now Snape."
The tall pale wizard looked to his mentor and nodded to him before turning his heel and Apparated away leaving the older long blonde haired wizard to his fate.
He found himself a short distance from the Shrieking Shack taking a moment to observe dilapidated building before he walked to the entrance.
Sirius Black almost killed him here years ago when Remus Lupin was locked up in their in his werewolf state and if not for James Potter he would have died. He angrily pushed back the thought taking deep breaths before he boldly entered the shack and found Voldemort waiting for him.
A conversation ensued with Voldemort musing on why his wand would not work.
Before he could react he found himself on the grimy floor feeling his life slip away, a dark blood pooling around him from the large open wound Voldemort's snake Nagini caused when she repeatedly struck him on the command of her Master.
Seconds, maybe minutes passed and he heard footsteps and looked up to the three students looking down to him. No gloating and only sadness in their eyes. They must have heard the conversation with Voldemort before the snake struck.
He felt a hand pressed firmly down on his neck and looked into the green eyes of Harry Potter. How those eyes reminded him of Lily.
"Take them." He gasped out pleadingly "Take them."
He watched Granger fumble for a moment giving Harry a phial so he could gather his memories that were leaking away in his death.
Dying, he felt pulled to the green eyes of the young man with the lightning scar. Whelp of his torturer during his time as a student at Hogwarts and suddenly realized the wizard before him was not at all like his father. Maybe they would succeed after all.
The pain from the venom overcame him and felt his life slip away more from the loss of blood. All of his memories of Lily came forth, her bright smile and the times they held before going to Hogwarts. How he loved her.
"Look at me!" He commanded weakly.
He caught Harrys green eyes, feeling death close.
"You have her eyes." He gasped out before closing his eyes. He felt death's presence draw closer to him. His last thought was the young wizard looking to him with sadness and regret was not of the father but of the mother. Í did the best I could for your son Lily. It is up to him now and I am sorry for how I treated you. I never got the chance to apologize before you were murdered. Murdered because of me because I was weak and full of hatred.
Harry, Ron, and Hermione watched Snape's body still and waited for a moment before realizing the professor was dead.
Snape opened his eyes and found himself not on the grimy floor of the Shrieking Shack but in the park where he met Lily. The times he spent with her there were the best moments in his life.
Looking around he found her sitting on a swing and rushed up to her feeling the weight of the past and his secrets disappear. He knelt down and took her hands into his holding them tightly and began to sob.
"Lily I'm sorry! It was because of me…." He began and felt her pull him close, sweet voice whispering in his ear.
You are forgiven Severus.