Is keeping a wife in this state, with no feelings of love or desire, considered an injustice to her for which the husband will be held accountable, or is it better to release her with kindness?

If the wife is religious and of good character, she should be kept with kindness, her company should be good, and her rights fulfilled. Among the most important of these rights is intercourse when she desires it and the husband is able. Marriage is not built on love alone, and a husband may dislike some traits in his wife, but she possesses other praiseworthy qualities; as the Prophet (peace be upon him) said: "No believing man should hate a believing woman; if he dislikes one of her characteristics, he will be pleased with another."

So, if it is possible to keep her with kindness, then do so. Otherwise, separate from her with goodness. Do not resort to divorce unless it is the better option, especially with the presence of children, due to its negative impact on them. Instead of divorce, one can marry another woman if the husband is capable of being just.