In season one, Haddie begins dating a boy, but hides it from her parents. She is also caught with drugs as she was trying to get attention as she has felt ignored her entire life due to her younger brother's behavioral problems.
She is seen closest to her cousin Amber (who has helped her with many issues). They temporarily fight after Amber sleeps with Haddie's boyfriend the night they break up, but they later reconcile.
In Season 2, Haddie volunteers in a soup kitchen where she meets Alex.
They become romantically involved, but her parents object to their relationship because they feel Alex is too mature for her, with too many "grown-up" problems (he is a recovering alcoholic who left an abusive home and lives alone).
Her parents' opposition to their relationship causes Haddie to move out to live with her grandparents.
The conflict is eventually resolved when Haddie returns home and Adam & Kristina grant her permission to continue seeing her boyfriend.
Haddie loses her virginity to Alex the night of her junior prom. Her parents find out when she misdials them while she is having sex.
During the beginning of the third season, Alex gets arrested and charged with assault after punching a guy at a house party. Haddie feels personally responsible since he was only there to pick her up.
Alex soon ends the relationship with her even after the charges are dropped because he feels that they are too different.
Haddie dedicates the rest of her senior year to school and gets accepted into Cornell. She leaves during the first episode of the fourth season and briefly returns to visit after learning about Kristina's breast cancer diagnosis.
To prevent her from worrying, Adam & Kristina tell her the cancer is benign and send her back to Cornell to live her dream college experience.
At the end of season 5, Haddie returns home for a visit with family with her friend Lauren. Max walks in on Haddie kissing Lauren, and it is later revealed that Haddie is in a same-sex relationship with her. Adam and Kristina are very accepting of this news and support her.