Why is Claudio so easily accepting Don John's lies about Hero's faithfulness? ACT 3 ONLY

Claudio easily accepted the lie told by Don John about the immorality and unfaithfulness of Hero because it was the matter of a life time relation. Relationship between a husband and wife are based on mutual thrust. Claudio do not wanted to take any risk in his life changing relation. The second reason can be lack of confidence of Claudio on his love.