Is it permissible to stipulate the continuation of marital life merely as siblings, while allowing the husband to marry another, in order to preserve the stability of the daughter, given the husband's drug abuse, lying, and betrayal?

It is permissible for a couple to agree to forgo intercourse, even completely, and the marriage remains valid. However, this agreement is not binding, and each party has the right to withdraw from it and demand their right to conjugal relations, because the right to intercourse is among the rights of the spouses that do not lapse except with their mutual consent. The wife is advised to treat her husband with kindness, strive for his betterment, and seek help from righteous people.