What is the Sharīʿah's view on the action of a husband who welcomed his wife's friend into the home and left her there during his absence, and what should the wife do to soothe her heart after her husband's admission of his mistake?

Seclusion with a non-mahram woman is forbidden by consensus, and it occurs when a man and a woman are alone in a place where they are safe from anyone entering upon them. Some scholars believe it occurs through a suspicious gathering. The husband erred by sitting alone with the non-mahram woman, but his repentance erases what came before it.