Belladonna Flowers are found on the Isle of Balduran.
|“||Odd-smelling flower, though very pretty.||”|
– Gorion's Ward
With Durlyle, you should be polite and romantic to gain his help (if you're impolite to him when accepting the cloak quest, you will NOT receive the Belladonna Flower quest after returning the cloak). He wants you to retrieve a cloak. Head to Dradeels cabin located in the northern half of the island. When you return you can insist on payment for the cloak if you cherish an extra 10gp but he will not help you later! Otherwise return the cloak for some tales. Talk to him again and he will ask for some Belladonna flowers. You should have found some in Dradeel's cabin but you can also pick some from two patches that grow just north of the village. He will tell you these flowers are for you, this prompts some romantic dialogue before he leaves.
If you hold these flowers, you won't be affected by the lycanthropy curse and thus won't die after several days if you don't kill Mendas when you return from the island.
(Note: The curse only affects Gorion's Ward and you have to speak with Mendas upon returning from the island for the clock to start)