What should a husband do who discovered that his wife is talking to a neighbor of his over the phone, knowing that their marital situation is on the verge of divorce, and that he loves her, and she has not met him [the neighbor]?

If it is confirmed that the wife speaks with a non-mahram neighbor, this is a grave evil and a transgression. It is incumbent upon her to protect her husband in his absence, as Allah Almighty says: "So righteous women are devoutly obedient, guarding in [the husband's] absence what Allah would have them guard."

The husband has authority over his wife, and he must obligate her to fulfill Allah's rights and prevent her from corruption.

The husband must advise his wife and remind her of Allah and His punishment, and warn her of the consequences of her actions, such as divorce and family disunity.

If the wife repents and becomes righteous, then praise be to Allah. Otherwise, divorcing such a woman is recommended, especially if she does not guard her chastity or does not preserve Allah's rights, because keeping her diminishes the husband's religiosity and there is fear of her corrupting his bed.