Disclaimer: I am neither blonde, 51, married, or rich. I do not have children and my name is not J.K. Rowling. Therefore, I do not own anything but the plot (if you can call it that).
Harry had always thought of his parents' deaths like a wound. For the world (both muggle and magical) it was nothing more than a scratch. Something that barely drew blood and itched when it healed, but it healed. There was no gaping wound, no giant scar. In fact, there was no scar at all. It happened and there was no point on dwelling on it. (Well, except for The-Boy-Who-Lived and He-Who-Must-Not-Be-Named is dead! thing.)
For him, Harry, it was a scar (maybe not a lightning bolt shaped one, but a scar nonetheless). It didn't hurt when touched, but it was always there. And unless someone pointed it out, he rarely even noticed it anymore. It was a scar that you got when you were to young to remember the act of getting it. One where you can never miss the unblemished skin, because you don't remember having it. One where you can't truly imagine not having it, so ingrained into your skin, your soul, your very being that scar is. One where the adults in your life constantly remark and reminisce on, until you've heard the story so many times that it's almost like you can remember it (or Dementors and Dark Lords force you to).
For Sirius, Harry imagined, it was a giant gaping wound. One that never truly stops bleeding, never truly heals. One that pains with every move, every breath. For Sirius, his parents death was a chunk of skin, of tissue, of muscle, and Azkaban was the infection. Harry likes to think that maybe Sirius would've been better (not fine exactly, never fine) if he hadn't been wrongly imprisoned. In some, not perfect, (his parents would still be dead) but better world. One where Harry grew up with Sirius and Remus and far away from the Dursleys, Harry likes to think the wound might've healed. It might've stopped bleeding and it never would've gotten infected with the poison that is Azkaban, but this isn't some far off distant world. As it is though, Harry likes to think that maybe he and Remus still help. That their belief in Sirius' innocence was some kind of antibiotic, getting rid of the infection. Harry likened himself to the stitches, keeping Sirius from bleeding anymore than he already had, maybe helping the wound start to pull together. Remus was the bandage, standing guard over Harry and Sirius, making sure nothing got in to hurt him anymore than he had already been hurt. (But then Avada Kedavra! and No! No, not Sirius! and who even cared anymore...)
Remus' wound, Harry always thought, was a mix between Sirius' gaping one and Harry's scar. For Remus, it was a massive scar, and (like Harry's) it healed, but (unlike Harry's) it was tender when touched. And (like Sirius') it bled, but (unlike Sirius') only occasionally. It would heal, but then something would tear it back open, (Peter's supposed 'death', Sirius' betrayal, you're a werewolf you can't watch Harry, the first full moon all alone, Black escaped!, Sirius' innocence, Peter's betrayal, you almost killed Harry, Harry's name in the Goblet of Fire, dragons, mermaids, Cedric Diggory is dead, The Order of the Phoenix without Lily or James, Umbridge, Sirius is dead!) and the process would begin again. It was a wound that never stopped hurting, that never fully healed. It was a giant scar across his chest, one that Remus hid and ignored when possible. (After all, Remus had lots of scars, what was one more?)
Author's Note: I would like to formally apologize for any and all punctuation mistakes and excessive use of commas and parentheses. Seriously, I know how annoying those can be, but I've never gotten the hang of commas, semicolons, and colons. I quite honestly don't think I ever will, believe me, many have tried to teach me. I would also like to apologize to those who liked my Batman story. I hated it, so I deleted the monstrosity. (I am also not usually this formal, but whenever I'm typing something, I go into Formal Essay or Email Mode.)