Loss runs throughout the Lord Of The Rings. Things given up willingly for the sake of others, or torn away savagely by a greater force. And no-one loses more than Frodo. At the start we see him giving up his happy life in the Shire, Often impatient with its inhabitants, wishing an 'earthquake or invasion of dragons' to wake them up, now they look very dear to him and to save them he leaves the Shire to go in to danger. But he keeps on losing. At Weathertop he loses his spiritual wholeness, his chance of ever being as he once was; 'That wound will never fully heal' Gandalf says to Elrond. In Moria he loses Gandalf, his beloved guide. and in Lothl?rien Galadriel tells him he must lose the friendship of the Fellowship.
It is not that he does not gain; a surprised and respectful Galadriel tells him he has gained a keen perception, and Faramir shows 'grave astonishment' at his courage and resolution. He is not the startled hobbit he was at Bree. But this insight only makes his losses harder to bear, and bring a greater understanding of what lies ahead. At Amon Hen Frodo loses Boromir to the Ring and the horror and shock make him realise he must go on alone.
But Frodo is no martyr. Like anyone he wants to live. He makes a last attempt to get rid of the Ring to Galadriel. When it is clear he must go on to the bitter end he makes a desperate attempt to save what is dearest to him; Sam. He leaves Sam behind. If Sam survives, something of himself will survive. He will have saved something back from the War, and the Ring. Sauron's mailed claw will not take everything he has. 'Look after Sam' he tells Aragorn.
But it all goes wrong. This was never in the script. Sam was meant to be with him. Gandalf told Frodo to take Sam with him, The elves of Gildor made Sam promise never to leave his master. Even on a practical level, Frodo would not have got far without Sam's sturdy presence and his pots and pans cooking up a 'bit of dinner'. Before they set off, Frodo said to him 'I might not come back' and Sam answered 'If you don't come back, neither will I'. But Frodo has to try.
Frodo never shows any sign that he thinks Sam might be tempted by the Ring as Boromir was. In Rivendell, when Sam urges Frodo to return to the Shire, he holds the ring out to his friend on his open palm. Sam glances warily at it then looks back to Frodo. His love for Frodo leaves no corner of his heart free for the Ring to infiltrate.
When Sam arrives on the beach and sees Frodo already far out on the water, he can't believe it. All the world honours Frodo's promise to take the Ring to Mordor, but he has to fight all the way to keep his promise to Frodo to be with him. Even Frodo has set it aside. Sam is devastated, and what is he to do how? Hang on the heels of the others while they pursue some other path? It would be the death of him. He cannot imagine not being with Frodo. When despite all their fine words and plans Frodo was brought near to death it was he, Sam, who watched the long nights beside his master's bedside in Rivendell, holding his cold hand. To Elrond he was just an eavesdropper and to Faramir a cheeky servant. But to the ones that mattered, Gandalf and Gildor and Galadriel, he was honoured as Frodo's true companion. And here he was, left on the beach. Sam had a favourite saying, 'drowned like a hobbit in a river'. Now he lives it out. Better to drown than be left behind. He wades out and throws himself in. When his clothes get soaked and drag him down he splashes about helplesly in the manner of non-swimmers, then goes under. He gives in to the water and sinks.
In the boat, Frodo can't believe it either. He had hoped to save Sam and now he was drowning. It was not the worst nightmare of Frodo's life, but a repeat of it; his parents drowned when he was 11. Now he was losing the only other family he had since Bilbo left. He reaches down and gropes in the water for Sam's hand and pulls him out. The elf-boat given to them by Galadriel steadies itself as he hauls Sam into it.
Sam is wet, angry and bitterly hurt. 'I made a promise!' he says desperately; if Frodo can't respect his loyalty maybe he wil respect his oath. Frodo has no answer just the tears on his face. He told Aragorn that Sam would not understand, and he doesn't. Frodo thinks Sam is signing his own death warrant, but he can't bear to hurt him any more by sending him back again. He seizes Sam and holds him tightly. He only left him behind because he loved him. But this time it is not Frodo's call. Nor even Sauron's. This time it is Sam's decision, and Frodo looks at him as at an equal. Now they really do share the same fate.