<P> Ryan Atwood is Marissa 's second boyfriend on The O.C. Although extremely on - and - off - again throughout the show 's course - their relationship originated as a platonic friendship in the pilot episode , which later escalated into romantic feelings . By the 10th episode of the first season , the couple officially began their romantic relationship . The beginning of this relationship sees its first end when Marissa feels that Ryan has overreacted to Marissa and Oliver Trask 's friendship . The second course of Marissa and Ryan 's relationship fails because of Theresa Diaz and Ryan 's illegitimate child together , whom Ryan agrees to help raise -- returning to Theresa 's arms and leaving Marissa to return to her alcoholic behavior . The third attempt of Marissa and Ryan 's relationship terminates after the suicide of Johnny Harper where they struggle to mourn him and need a break from each other . The couple 's last attempt at a relationship ends when Marissa is killed by a drunken Kevin Volchok who sends Ryan and Marissa 's carr off the road , sending her to her death . </P>
the oc when do ryan and marissa get together
the 10th episode of the first season