In The Two Towers it is love that makes Frodo leave behind the Fellowship so they do not get hurt by the Ring's evil; it is love that keeps Sam following Frodo into Mordor when Frodo says he doesn't have to come; it is love that sends Aragorn, Legolas, and Gimli after Merry and Pippin; it is love that allows Gimli and Legolas to develop their funny, bickering friendship; and it is love that leads Éomer to help Théoden as best he can, in spite of Wormtongue's lying. If Sauron uses negative emotions like jealousy, pride, and hatred as weapons, then love is the main weapon in the Good Side's arsenal. It's the glue that keeps them together, and—more importantly—going.
The true measure of a character's moral value in The Two Towers is not just the love that he has for others, but also the love that others have for him. For example, Boromir is a flawed character, but the affection that the good-guy Faramir shows toward his brother reminds us that at the end of the day, Boromir was a good guy.
By choosing to rescue Frodo rather than to continue the Ring quest on his own, Sam reaffirms his commitment to serving Frodo instead of achieving heroic fame for himself. Sam's final decision reestablishes the master-servant bond between Frodo and Sam.