Remus was a werewolf from a very young age. The transformation from human to werewolf is a very painful thing, and he went through it once a month for a good portion of his life. He probably did not have very many friends until he arrived at Hogwarts. There, he met his accepting friends, James Potter, Sirius Black, and Peter Pettigrew. During his time at Hogwarts, you can guess that he was happy. He finally had friends that really knew who he was, and accepted him. They all became an animagus so they could accompany him during the full moon. However, this did not take away the excruciating pain he had to endure once a month.
Once he got out of Hogwarts, he had the challenge of finding a job. Most people would not hire him, once they found out he was a werewolf. He could never hold down a job, and was poor.
Also, very soon after graduating from Hogwarts he lost all of his friends. Lily and James Potter were killed by Voldemort. Everyone was under the impression that Peter Pettigrew was killed by Sirius. And Sirius was sent to Azkaban. He was the only left of the Marauders. I can't even imagine what he went through on that Halloween. He lost three of his closest friends, and he believed his other friend was the one behind it. It's surprising he was ever able to get through it all.
Things did get better for Remus at one point. For one, Wolfsbane Potion was created and it relieved the pain of the transformations. Also, he found out that his friend Sirius Black was not the traitor. Albus Dumbledore was kind enough to give him the position of Defense Against the Dark Arts teacher at Hogwarts, his first real job. He met Nymphadora Tonks, fell in love, got married, and had a lovely son, Teddy Lupin.
He was killed, arguably during the happiest time of his life. So let's remember Remus Lupin, for fighting through the pain and fighting until the end.
