Disclaimer: JKR owns Remus. I own nothing.
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Remus Lupin allowed himself very few luxuries in life. After all, he was a werewolf. He knew from an early age not to get attached to anything too precious—the chances were always high that it would be ripped from his hands by the Ministry. Denying pleasure could prevent pain. As a young boy, there were no unnecessary toys or clothes in the Lupin household. The family survived only on what was needed. So he counted his riches in the most unlikely of places: friends that would stick by him despite what he was. For the seven wonderful years at Hogwarts, his friends were all he needed.
It wasn't long after Hogwarts that he had to readjust his life. He found that things as intangible as friendship, loyalty, and love were also held at a price he could not afford. The pleasure he had allowed himself ultimately led to the greatest pain—betrayal and death. Once again, he reevaluated what was important. The Ministry kept him from owning anything of value, and his condition kept immaterial treasures—friendship, loyalty, love—at arm's length. Remus decided that it was in his mind alone that he could count his blessings.
For twelve years he traveled, swallowing knowledge like a man dying of thirst. Some days he thought he was dying. Clothing, food, possessions… all were pushed aside for the sake of learning. His thoughts were beyond the Ministry's reach. And if he tossed and turned at night (haunted by phantom touches of friendship, loyalty, love), it was beaten away in the morning by the latest findings on Grindylows. His intelligence became a dark, heavy curtain muffling the glare of a moon turned red.
He resurfaced for air when he finally learned the truth. Remus realized that his mind was not always reliable, that investing in facts at face value would not always reveal the answer. Over the next year, he slowly cashed in his knowledge in return for a new currency, one he hadn't used since Hogwarts. His insight to the truth gave him loyalty, his memory of the past gave him friendship. And one stormy summer evening, love was returned for him to treasure. Once again, his life was complete simply because there was someone to share it with.
He should have learned his lesson all those years ago. He should have remembered that pleasure only brought pain. In one graceful fall, everything he had of value—friendship, loyalty, love—was ripped from his hands. And he remembered that Death had a stronger grasp than even the Ministry.
Remus Lupin allows himself very few luxuries in life. All of his possessions can fit in a single, broken suitcase. He has no bank account at Gringott's, no stash under his mattress. He contributes what he can to the Order and the fight against Voldemort, but his knowledge belongs to an old man with sharp eyes. The only things he values were found in a trunk left behind by a sixteen-year-old runaway over twenty years ago, and now are tucked away in a pocket next to his heart. Every night he places them gently on the table next to his bed, whispering names in remembrance before drifting to sleep. A green ribbon (friendship), a photograph of two black-haired boys (loyalty), a half-written note in elegant scrawl (love). He cannot find value beyond his memories. Everything else has been taken from him, and he has no other choice.