Greendale in Chilling Adventures of Sabrina is a lot like Sunnydale in Buffy — full of really pretty people who are bound to get hurt in some terrible ways. For some of them, the hurting is literal and they meet their grisly end (RIP real Miss Wardwell), while others get emotionally devastated. Harvey Kinkle, our sweet, precious coal-miner's son, is a frequent sufferer of the latter. Though much of season one focuses on Sabrina's love for Harvey and her attempts to make his life better in any possible way, it massively backfires and leads to their eventual breakup. It also results in Harvey losing his nearest and dearest, his big brother Tommy, in the most heartbreaking way.
When we meet Tommy Kinkle, it's obvious that Harvey idolizes him, and for good reason. The eldest Kinkle is sweet, thoughtful, and protects his brother from their father's temper — usually directed at Harvey for going to school and not working in the Greendale coal mines. Tommy encourages Harvey to pursue his art, passing up on college to work in the mines with their father himself so Harvey can be free to attend school. Basically, Tommy is the best person ever and doesn't deserve anything that happens to him later in the season.
The events that lead to Tommy's demise begin in episode seven, "Feast of Feasts." Prudence, who is staying with the Spellmans while Sabrina acts as her handmaiden before the annual Feast of Feasts, discovers that Harvey is the descendant of witch hunters. Worried about what the Weird Sisters might do, Sabrina casts a charm of protection over Harvey. This turns out to be a wise precaution when Agatha and Dorcas perform a ritual to kill Harvey and Tommy in a mine collapse. In episode eight, we learn that because of Sabrina's spell, Harvey is saved, but Tommy is killed along with four others. When Sabrina learns that Agatha and Dorcas were the ones behind the mine collapse, she recruits the aid of Prudence and Nick to strong-arm Dorcas and Agatha into resurrecting Tommy and replacing his soul with Agatha's. Sabrina believes that she can use the Cain Pit in the cemetery of the Spellman Sisters' Mortuary to bring her back to life and loophole the balance of life (even mortals would know that's a bad plan).
Surprise! You can't cheat death, and Sabrina learns this the hard way in the following episode, "The Returned Man." Though Tommy has indeed risen from the dead, he isn't the same Tommy that was killed in the mines — he's basically a human shell. Both Harvey and his father sense the difference in Tommy, the eldest Kinkle, and his father finds solace at the bottom of a bottle rather than trying to deal with either of his sons. Sabrina figures out that Tommy isn't whole because his soul is in limbo, where she unsuccessfully tries to retrieve it. Unfortunately, his soul is snatched by the soul-eater and Sabrina realizes that the only solution is to kill Husk-Tommy (which everyone has been telling her since this began).
Resigned, Sabrina tells Harvey the truth — she's a witch who used her magic to resurrect Tommy, but brought him back without a soul and now has to kill the shell that is his body. Harvey is understandably in shock and desolate; he tells Sabrina that she shouldn't have done anything and he will be the one to kill his brother. Also understandably, he ends his relationship with Sabrina, telling her he can't look at her without seeing his dead brother's face. Though the two seem to make steps to some kind of reconciliation, by the time we get to the holiday special, "A Midwinter's Tale," it's still super awkward (again, understandably, since she basically made him kill his brother).
Sabrina gifts Harvey with an enchanted colored pencil set, which is charmed to never need sharpening. He hesitatingly accepts the gift (he doesn't give one back which is kind of bad manners, but still, we get it), and offers her a "Happy Solstice." Later, because Sabrina really doesn't know how to stop meddling even though Harvey explicitly told her not to use magic without telling him, the young witch appears at the Kinkles's doorstep with some eggnog that is spelled to make Harvey's father turn away from alcohol forever. When Harvey approaches her on Christmas Eve, he tells her that, while he appreciates her trying to help, she has to stop doing magic for or around him. He specifically says, "Don't use magic with me or on me or near me," telling her that he just doesn't trust it. Which again, we totally get. We doubt we'll be seeing poor Tommy again in season two, but considering this is Chilling Adventures . . . you never know.