Poor little Fanny Robin is probably the biggest victim in this entire book. The first thing we ever learn about her is that she is very poor and she is trying to leave Weatherbury to track down Sergeant Troy, a man who has promised to marry her. As she says to Gabriel Oak when he gives her money, "Thank you indeed […] I am rather poor and I don't want people to know anything about me" (7.31). Fanny is also a very proud and fair woman, though, and at the first opportunity she gets, she sends Oak some money in the mail to repay her debt to him.
On top of being brave, Fanny is also very modest and very frail. She's basically got the word "doomed" written all over her. She's just too good and too innocent to survive in Hardy's harsh world. We can see the clouds of doom rolling in when Fanny begs her lover Sergeant Troy to marry her, saying, "O Frank—you thin me forward I am afraid! Don't dear Frank—will you—for I love you so. And you said lots of times you would marry me, and—and—I—I—I—" (11.52). Sergeant Troy, though, ends up totally blowing her off and marrying the rich Bathsheba Everdene instead. Sergeant Troy is not a good dude.
We don't actually get to see the really sad stuff, where Fanny has Troy's baby, has no money, and is forced to walk like a gajillion miles to the nearest poorhouse. And that's just as well, because we'd probably go through several boxes of Kleenex (and then several pints of Ben and Jerry's to make ourselves feel better).
It seems that only in death can Fanny finally make Sergeant Troy understand how deep their love is. As he bends over her coffin, Troy kisses her face and cries, "But never mind darling […] in the sight of heaven you are my very very wife" (43.76). He even buys a huge tombstone to commemorate what a wonderful person Fanny was. The only problem is that he's only able to realize this after she's gone forever.