Does a husband's suspicion regarding his wife's frequent outings with her relatives without his permission, and the possibility of her staying overnight at her aunt's house, justify a sin on his part, and is the wife sinful for these outings?

It is not permissible for a wife to leave her husband's house except out of necessity or with his permission. If she goes to her family's house, she is not permitted to leave it except with his permission. She must obey him if he forbids her from going out, unless it involves disobedience [to Allah]. The husband is advised to cast away misgivings and to have a good opinion of his family.