Background
During our last game session, one of the characters gathered enough Shadow to equal their max hope- there was not enough time to Harden Will so hit his max cap.
was running with 10 hope, 6 shadow and 2 scars, got hit with a Great Cave Trolls Strike Fear ability and failed the roll, gaining 2 Shadow
after an earlier fight, the party found a magic bow of Númenórean craftsmanship [that was due to become one of the characters items from the Treasure Index]
What happened after
the player looked through the Madness section and decided that as he was a Ranger of the North and had planned to take Royalty Revealed during the next Fellowship Phase, he would take a bout of Lust and steal the new magic bow as it was "his due, as he was descended from Númenóreans". When the Party camped for the night to recover from the Troll fight, he made a Stealth roll and succeeded with a 6 then hid it for later retrieval. When the party woke up I told the player that her new bow was missing - a number of Scan and Hunting rolls were done by the party but no one rolled a 6 so didn't beat the thief's number of successes.
So the question is, AITA for letting this happen and letting one character steal from another when undergoing a Bout of Madness?