[Corwyn Celesil]

Ah, why did Sam go? Why did he do what he did? First it was duty, I believe. Tolkien had an intrisically British worldview, mainly pre-WWII worldview since that was when he was a child and young man, and his automatic views on masters and servants came out in it. Mister Frodo was the master, Sam was the epitome of the devoted servant; both knew it, and neither found anything wrong with it, just as generations of lower, middle, and high-class Brits never found anything wrong with it. At first Sam was devoted to Frodo as any really good servant would be. Later I believe it became a really intense brotherly kind of love. "Greater love hath no man than this: that he would lay down his life for his friend."
And of course Sam was afraid! He was the simplest of hobbits, the most home-loving, security-loving of hobbits. After looking into Galadriel's mirror, he knew well the impact of the Ring. How easily he could have turn around and run home, or stayed in Rivendell or Lothlorien! But Sam had that which was deeper than his fear: a knowledge of what was right, and a determination to do it. Perhaps his fear spurred him on to do what was right rather than fleeing from it. But courage is not the lack of fear; it is doing what needs to be done despite fear. So Sam was all of the above: a loyal servant and friend, purely scared, and purely brave. He would not have seen himself as brave, for his fear was always with him, but yet he still went on.