Reason: Theresa's former fiance, Eddie, arrives in Newport to talk Theresa into going back to Chino, to which she eventually accepts. As Theresa and Eddie are once again engaged, Ryan's relationship with Theresa comes to an end.
Reason: After living together for the summer and realizing that Ryan is unhappy, Theresa ends her relationship with Ryan by lying saying she had a miscarriage so that he would go back to his life in Newport. Despite their break-up, the two remain on good terms with one another when they reunite as friends at the end of season two.
Reason: Ryan attempts to inform Marissa of Oliver's lies and his unhealthy obsession with her, though she refuses to believe him. After repeated attempts to get her to turn against Oliver, Marissa breaks things off with Ryan.
Reason: After discovering that Theresa is seemingly pregnant with his child, as the two had been in a relationship, during Ryan and Marissa's breakup, Ryan decides to move back to Chino with Theresa despite his feelings for Marissa.
Reason: Despite Ryan and Lindsay's tendency to constantly put their relationship on a break, the two did not actually break up until Lindsay decided to leave Newport for Chicago, where her mother was moving following the exposure of her affair with Lindsay's father, Caleb Nichol.
Reason: Sadie said that nothing was keeping her in Newport so she decided to leave to Oregan just hours before Ryan came to her house with flowers to ask her to stay. *EDIT: Marissa actually went to the bus station and told Sadie how happy she made Ryan. Sadie didn't leave/ They didn't break up until the sweatshirt party.
Reason: Ryan did not adjust to living in France with Taylor while she attended Sorbonne. They have sex when she arrives in Berkeley, but their relationship status as the series concludes is left in the air.