Written after 'Order of the Phoenix' but doesn't contain any (obvious) spoilers.
He is nine years old and his best friend has dared him to kiss Amelia, who lives next door to him. She is sitting in her garden with her friend, and he walks over and tells Amelia he wants to talk to her. When she stands up he kisses her and she pushes him away in disgust. He isn't terribly bothered; he's fulfilled the terms of the dare and he doesn't really see the point in kissing, anyway. They walk away laughing and James talks about how weird girls are, then he starts thinking about a dare for his friend.
He is in his first year at Hogwarts and when he goes home for Christmas his parents are having a party for their friends. He sees one of the boys from school there, and even though he's a seventh-year and looks sort of scary, Peter goes over anyway because the boy looks as bored as he does. He has pale white-blonde hair that falls into his face when he kisses Peter, who is surprised at first, but after a while he starts to like it and they go upstairs and he does everything the older boy tells him to do.
He and James are up late one night talking in the Gryffindor common room when Sirius confesses that he has never been kissed. He is embarrassed at first, because he is thirteen and acts like he knows it all already, and he knows that James is the only person he can trust with this secret. At first he thinks James is going to laugh, but instead he says that he doesn't see the point, really, because girls are so annoying and act so stupid. Sirius agrees, but he still wishes he knew what it was like, so James shows him.
She is invited to a sleepover the older girls are having because she's friendly with one of them and she can't help but notice the quiet blonde girl sitting with her knees pulled up to her chest. She is dared to kiss her, and even though she panics at first, she is not one to pull out of a dare and so she leans in and presses her own lips against the girl's. After a moment she gathers enough courage to slip her tongue between the other girl's lips, and when she is finished she gives her a tentative half-smile.
He refuses to tell Sirius that he's jealous of his close friendship with James, but eventually Sirius confronts him about it and he is forced to reveal the truth. Sirius stares at him in surprise for a moment before declaring that there is nothing going on between him and James, and as if to prove it, cups Remus's face and brings it close to his own. Their lips meet, and it is a shy kiss at first, but this is what Remus has wanted for six years, and when they finally break apart, his lips are bruised. He smiles shyly.
He doesn't like that she feels sorry for him, and he tells her that. He doesn't want to be pitied. Lily looks at him and says that she hasn't felt sorry for him in a long time. He knows how to take care of himself. She'd like to be friends, though, because she thinks he's interesting. And attractive. He frowns at that, sure she is mocking him, but instead she brushes a finger across his lips and then kisses him. He jumps back in surprise and she looks hurt. He kisses her clumsily but enthusiastically to make up for it.