Anyway I'm thinking of Tommy and Buck in Sunnydale, Buck as a freshman whose sister Maddie is a senior and the Slayer and Tommy as a senior and football vice-captain. Bobby is her Watcher and Athena the chief of the local police department, so she can decide who works on which cases.
And the thing is that Maddie and Tommy became friends in freshman year because she saved his life from a vamped cheerleader, and he keeps her from being harassed by the others because he's literally the Coolest Hottest Football Star in school. He disapproved of Doug but Maddie was stubborn about it, saying she liked being "just a girl" with Doug (who knows Maddie is very strong and uses that to get her to "behave more like other girls").
Tommy's lab partner Chim likes Maddie but he also knows not to force the issue. Karen is basically gonna be valedictorian, everyone knows that, and Hen finds her annoying (that means Hen can't stop thinking about her), and Tommy loses $20 to Chim when Hen and Karen finally kiss in one of the life-threatening encounters
Tommy gets to know Maddie's younger brother back when he was just a kid, so he always sees Evan as a kid. Over the holidays between Tommy's junior and senior year, Maddie ran away after her boyfriend Doug tried to kill her (and he wasn't even a vampire, just evil) and she had to kill him in self defense, and the Buckleys basically fell apart; Evan went away with his parents until the school year began and he comes back as a freshman but Maddie is still missing. Evan gets picked on for being Murdering Maddie's brother and Tommy takes Evan under his wing, lets Evan hang with him and even trains Evan well enough to play football so he can keep an eye on the kid.
Except feelings grow and they do end up dating in secret. Evan's first kiss and his first time having sex are with Tommy, and Tommy feels guilty because he hasn't come out to anyone and he doesn't want to, because if he does he's gonna lose his vice-captaincy and maybe a football scholarship.
But then football captain Larry comes out, and Tommy realizes that maybe he can come out too, but before he does, Maddie comes back and she disapproves of Evan being involved in the slaying biz. Days before graduation it all comes to a head and Tommy and Maddie clash about it. Then the big secret is revealed and Maddie's too shocked by it and the Buckleys are so furious, they threaten to call the police on Tommy to accuse him of sexual assault on their son, and Tommy runs away from Sunnydale via enlistment in the army after the big battle.
It's only until college that Evan (Buck by then) meets Tommy again — except Tommy is now in the Initiative















