He’s easily fooled by eloquent words, but how would he know otherwise if he didn’t doubt? Perhaps a kinder label would be “trusting”, or even “naive”, but he is neither of those things, because he wouldn’t live alone if that were so.
He becomes afraid of lies, and consequently rejects everything in the smallest chance that the lie will come true. It’s always better to be safe than sorry, and this way, he’ll always be safe.
He’ll always be alone, but that’s something he’s already used to, and so he casts away everything for the sake of his peace of mind.