Epilogue-Merry's Promise
Merry realized that Pippin was perfectly able to take care of himself. He had realized it after being found, bloody and injured, on the fields of the Pelennor. Far from being unhappy at this realization, Merry simply accepted it. He knew, this time, that he was still needed. He had always known that Pippin needed him, and he knew now that he needed Pippin just as much.
After the War of the Ring was over, and Frodo and Sam were returned to their friends and family, both Pippin and Merry tried to help them as much as they could. They all needed each other, as friends naturally do, and likewise, they all knew that Frodo's return might only be temporary.
Frodo once hinted at this when he whispered to Merry and Pippin, "Whatever happens, promise me you will look after Sam, and after each other."
Knowing that his older cousin was planning his own leave hurt Merry's heart…but it did not break it. He had wanted to help Frodo in whatever way he could, and he had. Frodo would do what was best for him, and they would take care of Sam.
Frodo and Sam were best friends, and they were meant to look after each other. Despite whatever parting the Hobbits had on Middle-Earth, Merry and Pippin both understood that they would all see each other again.
Merry's promise was one he never broke. He and Pippin looked after each other, happily, until the end of their days.