Both Holden and Sally reflect being in different places in different times, and yet being in a relationship.  Usually, such a configuration does not always work out for the best.  This is no exception.  Sally seeks a more traditional path in how she conceives of their relationship.  Her insistence on college coming first and a more conservative approach to their relationship is in direct opposition to Holden's vision.  His conception of the romantic good is one where definition is not really clear.  Part of this is because he is not entirely clear about much in his own life, and this is transferred onto their relationship.  Holden does know that he disdains what others consider "advantageous," and seeks to find a new path that has not been traversed.  In this light, Sally's suggestions are rebuked because there is little authentically new ground featured within them.  In this light, Holden does not share the same understanding that Sally does.  This might not be a reflection of a bad relationship as much as it displays Holden's own sense of loss, insecurity, and doubt about where he is in the world and his place in it.