Why a Doe symbolizes Snape's love for Lily when in fact it symbolizes the tragedy of his life?

Question

I know it was her Patronus. But.

As JKR stated in an interview:

Chely: James patronus is a stag and lilys a doe is that a coincidence?

J.K. Rowling: No, the Patronus often mutates to take the image of the love of one's life (because they so often become the 'happy thought' that generates a Patronus).

Meaning Lily's Patronus does not represent her personality as Snape knew it. Apparently Lily's Patronus would be (or was - if she mastered it earlier) something different, more personal. Obviously Snape's Patronus should have changed together with Lily's from being something different before (if he could cast it by the time).

Doe is the evidence of Lily's love for Snape's worst enemy - probably the worst thing happened in Snape's life apart from her death. How does this represent the happiest thoughts for Snape? Basically, Snape's Patronus mutates to match James's - which is just bizarre, especially when you think that Snape should be aware of it.

Side thoughts: Patronus probably should not necessarily take form of your love's Patronus to match. We see Tonks cast a wolf when fall in love with Lupin - probably just because a wolf is something that associated with him in her mind. I doubt that Lupin's Patronus is a wolf, given he should consider it to be the most hated part of himself. So Patronus should be more about your own perception of the loved one (speculative though). So... why a doe?!

Answer 1

As it was already answered here Snape had the same patronus as Lily, because he was in love with her. For all those years - his love was pure and unconditional:

"But this is touching, Severus" said Dumbledore seriously. "Have you grown to care for the boy, after all?"

"For him?" shouted Snape. "Expecto Patronum!"

From the tip of his wand burst the silver doe: She landed on the office floor, bounded across the office, and soared out of the window. Dumbledore watched her fly away, and as he silvery glow faded he turned back to Snape, and his eyes were full of tears.

"After all this time?"

"Always" said Snape.

For Snape it doesn't matter that Lily's patronus has changed to match James one - it is still Lily's patronus, something that is expression of her hope and happiness; it still comes from the person that he loves. So while it most probably hurt Snape, that Lily's patronus has changed (same as it hurt him, that she has chosen James - someone he hated), in the end it didn't matter to him as long as Lily was happy.

Even more, please notice that Snape's patronus is EXACTLY the same as Lily's one. In contrast, note that while similar - Lily's and James's one differ not only in gender, but in specie - doe is not "female stag": "stag" is a male red deer, female is "hind", male version of "doe" (a roe deer) is "buck". This shows how deeply in love he is.

Answer 2

Snape thinking of Lily's safety without really considering her family is more unthinking panic than anything else, in my opinion. Harry was the reason Voldemort was after Lily, more an object than a person in their minds. And of course he hated James.

Still, I should think it wasn't malice so much as his attention going to the thing that mattered to him. Lily was going to die. If I heard about a hostage situation on the news, I'd be disturbed, concerned, etc., but if I heard that my sister was in there? My thoughts would be "Get HER out alive." I'm sorry, that's how I'd feel. It isn't even abnormal.

To his credit, when Dumbledore hinted that the family, not just Lily, should be protected, Snape accepted the Headmaster's condition without hesitation. She'd chosen a husband that he hated passionately. Another man might have said, "Serves the bi--h right," but he still cared enough to face both Voldemort (who was mercurial at best, even with his favorites) and Dumbledore (who he feared would kill him on sight, but still met with and agreed to spy for).

Is a matching Patronus the sign of true love? I don't know. James's stag was similar to Lily's doe (although it's already been pointed out they aren't quite the same). Maybe the similarity caught Lily's attention. She may have thought it implied they had more in common than she'd previously believed. When she gave James a chance, it turned out to be true, which led to their eventual marriage. Snape having the same doe may show the depth of her effect on him more than true love or obsession. Her friendship was so precious, even after he lost it, that Lily Evans literally helped mold the man he became. Maybe that's why the thought of her could remain his most joyful memory. She made him better than he'd thought he could be.