Sean Donahue, the son of Nancy Donahue, is Axl and Darrin's best friend and teammate on the football team. He was employee of the month at his job and is from a "perfect family."
He is helpful, polite, and friendly, which makes him outwardly the opposite of Axl. He always supports everything Axl does. Although Axl assumes the leader role in their group of friends, Sean is the smartest of the three. He gets good grades and was accepted to Notre Dame.
Despite being very nice, he has a mean inside, you can clearly tell when Sue cant go to prom with him, he is all smiley but in the inside he is furious, he always mentions that Sue can be a very frustrating person.
In season 2, Sue developed a crush on Sean, but eventually ends the one-way relationship. They end the series married.
In season 7, Sean goes through a "hippie phase" during which he is a vegetarian.
In The Walk, Sean Donahue came to the Heck House and told Sue that Frankie was telling Nancy that Sue didn't have a date to prom and that that's crazy and felt obligated to take her. Before Sue could speak, he explained that his car broke down on the way from college and he's missing a major class but it's okay and she's like family. Sue felt touched. Sue had too many dates and declined him later which he acted smiley but was a little upset. He told this to Darrin who realized Sue had too many dates.
It wasn't until Exes and Ohhhs where Sean showed signs of really really liking Sue, and has for a long while. Yet, sadly more mistakes occur, just like Sue and Darrin in The Walk, the two lovebirds didn't get to confess. Sean is shown multiple times, coming back to confess to Sue but more awkward events occur. Sean and Sue have a stronger liking for each other at this point than ever before.
In Please Don't Feed the Hecks, Sean casually visits Sue at East Indiana University, when she finds out that she and Lexie were kicked out of their college apartment after it was sublet to a man who refuses to leave, and who also turns out to be one of her professors. Despite Sue and Lexie's effort to devise a plan, with help from Brad Bottig, Sean visits the apartment and threatens to spread a rumor that he and Sue are having an illicit on-campus affair. Though grateful for his intervention, Sue is upset that her effort to expose herself as a strong feminist icon, and dreads the idea that his rescue plays into the stereotype of the damsel in distress being rescued by prince on the white horse. Sean then reminds her of an incident where he got stuck in a drainage pipe he was forbidden to play in, and she rescued him with her jump rope, never revealed the incident. Sean summarized that gender and gender roles have no relevance over who rescues who.
In The Christmas Miracle, Sean finds out he has 3 Bs and 2 “the thing that comes after B” (C), which means the for the first time in his life he has grades below an A, which isn’t normal for him as he’s a Donahue. Sue comforts him and tells him all about her experiences as being “average” and “middle of the pack.” The two are passionately kissing at the end of the episode as the snow falls around them in the Hecks’ back-garden.
In A Heck of a Ride, Sean is about to go to Ghana when he finds the snow globe Sue gave him in his bag. He leaves the airport and tries to catch up with Sue, who is on the road taking Axl to Denver. He confesses his feeling for her and she does the same. They kiss and we later find out that they broke up and got back together multiple times before finally getting married.