Is it permissible to request a divorce due to harm, and what are the consequences, if the husband discovers his wife's infidelity after seeing her romantic pictures and conversations with her lover, and neighbors confirm her lover's entry into the marital home?

You should not keep this woman if she does not repent with a sincere repentance. You must separate from her, either through divorce (ṭalāq) or khulʿ (a form of divorce initiated by the wife). Separating from a wife who is neglectful of God's rights or who is not chaste is recommended, and may even be obligatory. You are permitted to make things difficult for her so that she forfeits her dower (mahr) or a portion of it.