Is it permissible to separate from a fiancé who smokes, is negligent in his prayers, and practices masturbation, after failed attempts at reform, especially given prior psychological pressures regarding marriage following the dissolution of the first engagement? And is it legislated to perform Istikhara concerning separation?

If the marriage contract has been concluded, the couple are considered married. It is not permissible for a woman to seek divorce without a valid reason, but the husband's impiety and his negligence in fulfilling Allah's rights and prayer permit her to seek a divorce. If the wife has made an effort to advise him and reform him, and he has not responded, then there is no blame upon her for seeking a divorce; in fact, separation is recommended. If the husband completely abandons prayer, then the wife must seek a divorce, and it is not permissible for her to remain under his marital bond.