All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is impermissible for the husband to accuse his wife of committing immorality based on mere doubts and inner thoughts! The Islamic Sharee'ah forbade doubting the wife's chastity, searching for her faults, and thinking ill of someone whose actions are not suspicious. Please, refer to fataawa 21021 and 87877.
If the husband fears that his wife may have been infected with a contagious disease and his fear stems from a valid reason and not mere doubts, then he may try to convince her to have a medical checkup without accusing her of having committed adultery.
If a man suspected his wife's behavior and has good reason to believe that she is most likely not a chaste woman, then he should not hesitate in parting with her in order to safeguard his honor, religiosity, and health.
Lastly, we would like to point out that the husband should fulfill his duty of Qawaamah (guardianship) over his wife, protect her from potential temptations, spare her the evils of meeting in seclusion with non-Mahram (marriageable) men and impermissible intermixing with them, and then think well of her. He would thus safeguard her from temptations and block the way for the devil and his evil schemes to lure her into sin.
Allaah knows best.