Sandy and Soda had been a couple for awhile when she got pregnant and went to Florida to have her baby. As it turns out, Soda wasn't the father - in explaining what had been happening to their brother, Darry tells Ponyboy, "He told me he loved her, but I guess she didn't love him like he thought she did, because it wasn't him...He wanted to marry her anyway, but she just left". Soda still loved Sandy even when it was evident that she had cheated on him, but Sandy didn't feel the same way about him. Soda wanted to marry her, but she just disappeared, and his letters to her were "returned unopened" (Chapter 12).
Early in the novel, Ponyboy is under the impression that the love between his brother Sodapop and his girlfriend Sandy is mutual. Because Ponyboy idolizes Soda, he imagines that Sandy feels the same way. Later in the novel, however, it is revealed that things are not right between Soda and Sandy. In chapter seven, Soda tells Ponyboy that Sandy has gone to live with her grandmother in Florida, presumably because she has become pregnant. Steve suggests that the baby is Soda's and that Sandy's parents had no intention of letting her marry the boy, who is only sixteen. Later, in chapter twelve, Darry tells Ponyboy that Soda was not the father of Sandy's baby and that it was someone else. Regardless of this, Soda is still willing to marry her, but Sandy obviously didn't love him as much as he loved her. She returns his letters unopened, which sparks Soda to run out of the house after an argument between Darry and Ponyboy. Darry says, "He told me he loved her, but I guess she didn't love him like he thought she did."