Harry doesn't know when he realized.
It's Hermione, after all. She's frizzy haired and bossy and she gives the best hugs and smells like books and ink and she's crazily opinionated and she stays up late with him and makes him talk about anything and everything that's bothering him because she has this uncanny sense when it does, and she's pretty and she kissed his cheek that one time and her voice is in his head all the time and oh God, Harry loves her.
Because it's Hermione, after all, and she's never left his side and she saves him toast and treacle tart and worries about him and buys him expensive broomstick polish and when she smiles at him, his heart might just burst and he can't bear to see her cry and she's always his first priority so he leaves everything to go to her when she asks him too. And maybe that was because they are friends and friends do that, but Harry never feels his heart swell up when he sees Ron fell asleep on the couch on his arm; he shakes off Ron and throws him to the ground. So yeah, it's Hermione and she's crazy and irritable and she carries the weight of his troubles on her back with him and she wears his quidditch jersey with his name on her back to all the quidditch games and that makes Harry want to fly down after catching the snitch and kissing her infront of the whole school.
Now they are at a Quidditch game and it's Gryffindor vs Slyherin and he's the Captain and this will win them the Cup. He's down at the locker rooms and the others are changing and Harry's feeling nervous and nauseous and excited. He's pacing outside and his thoughts are a flurry of sand storms or something and then Hermione's coming towards him and she's wearing his jersey and her hair is held back a bit by two small braids. The POTTER emblazoned on her back as she hugs him makes his heart flip and he buries his nose into her neck as he lifts her up in his arms. She's here and she's soft and he's taller than her and she smells woodsy like a campfire his name is one her back and her hair is golden with burnt red tones and he's such a sap for thinking all this. She pulls back from the hug but Harry doesn't let her go; she giggles and kisses his cheek and says, "You'll be fine, Harry." Her smile makes it hard for him to focus on much anyways, so he nods dazedly. She's in his arms still; he's holding her in his arms and it feels absolutely dreamy and Harry really wants to kiss her smile.
The players come out of the rooms in their Quidditch robes and Harry's pretty sure he was supposed to be worried about one of the Weasleys but he can't remember who or why. Then Hermione's stepping away and yelling good luck to them all as she walks away and her shorts are hidden by his big Quidditch jersey and Harry can't stop staring at her legs.
He shakes hands with the Slytherin Captain and they're off and Luna Lovegood is doing the commentary again. He's starting to enjoy her distracted words anyways. He focuses on his role, on the match. He has a trophy to win.
The match is hard and it's close sometimes. Slytherin is Slytherin and they are really good at Quidditch. Ron's playing pretty well today; he's let some goals in but he shook it off and Harry's proud. Their Quidditch team might not have the experience and talent of the previous line ups but they are good and in some time would be as great as their predecessors. They hold their own against Slytherin and Harry's looking for the snitch but it's taking awfully long to appear today.
Then suddenly, as he's up above and surveying the game, he passes a spot and blinks then passes it again and he sees it. A flash of gold and Luna's still going on about some dirigibles or something like that so he's certain no one else has. He speeds up casually taking a small loop and he's nearly there when the spectators realize it. People start pointing and there's chaos and Luna's serene voice is still serene and she's talking about radishes and snitches and the slytherin seeker Harper is way better than Malfoy and Harry can see him coming towards the snitch, superbly dodging a bludger and the quaffle. There's a slytherin beater approaching from Harry's other side and he knows he will know him out so he pushes his Firebolt to greater speeds. He hears a whistling sound and looks up and the budget is coming for his head and he loops and dives and does a twirl while maintaining his speed and he's proud of himself honestly; and a part of him hopes that Hermione was impressed. Then he does something stupid and reckless; the snitch is a flashing blur and Harry's twirl made him loose valuable time. And there's another bludger coming- where the fuck are his beaters- and Harry lets it sail by and then tries to grab it and nearly succeeds; or atleast succeeds enough to get a much needed momentum. And then his hand is stretching out and he thinks he hears Hermione from the stand and now his fingers are wrapped around the tiresome ball and he pulls out of the dive and in his hand is the snitch. And Gryffindor wins, 300 to 120 and the stands erupt and Luna has produced the lion hat from last year and it's roaring. Then the captains are shaking hands and the gryffindors are swarming him and the team is holding the Cup and McGonagall looks proud of him. And there's Hermione and she's jumping and waving at him and in all the euphoria Harry has the whim: he's going to kiss her, goddammit. So he mounts his broom and he flies to her in the stands and she's wearing his jersey and he loves her and then he's infront of her and Harry's grinning so hard his cheeks hurt and he says hi and she smiles harder and then she's throwing her arms around his neck as he dismounts and his brooms falls as he picks her in his arms and he doesn't really care. Her legs are wrapped around his waist and she's kissing him and she tastes like coffee and mint and Harry finally gets what addiction is because he is addicted. She's all he can see, taste, smell, feel or think of and Harry never wants to stop kissing her. He deepens the kiss and she mms against him and fuck breathing, who needs to breathe when there's the option of kissing Hermione. Harry would've been content to stay there, kissing her forever but then they pull apart and Harry's grinning wider than before, which no one thought would be possible. And then everyone's cheering for them and he seeks out Ron in the crowd and he has a small grin on his face and he gives Harry a thumbs up and Harry's glad for he didn't want to lose Ron. He meets Dumbledore's eyes next and his eyes are twinkling and he has the look where he just got proved right. Even McGonagall has a slight smile even as she stakes her head disapprovingly and oh God, did Snape have an approving look on his face?
Whatever, who cares. Hermione's in his arms and she kissed him and they should talk and they just won the Championship. He tucks a wavy tendril behind her hair and she's smiling and he kisses her smile again because he can do that now. He pulls away and raises his eyebrow and because she's Hermione she gets it and she shrugs and says, "By the lake?" And Harry nods and picks up his broomstick and takes her hand in his other hand and pulls her through the crowd. They walk out of the cheering crowd, pushing and trampling and almost getting stomped on.
Harry looks down at Hermione's beaming face, as they sit down by the lake, and then she leans up to kiss him and he suddenly realizes that this would now be his Patronus memory: Hermione leaning up to kiss him.