Astarion was so shocked by your request that he couldn’t really find the words to respond.

Over his long life and his tragic history of violence and servitude, he was accustomed to using his body to satisfy the requests of his master. Seducing and luring people wasn't a problem - it was his everyday life, a routine. Despite the initial internal resistance and shame, over time he came to terms with it.

So when you asked him for a simple hug - and nothing else - you caught Astarion off guard.