Should I continue an engagement that involved deception regarding housing and in which I was subjected to abuse from the fiancé's mother, or is it better to terminate the engagement?

Do not rush to seek divorce. Instead, be patient with your husband and help him resolve the issues in his home. As long as the marriage contract has been concluded, you cannot annul the contract except through khul' (divorce at the wife's instance with compensation) or by asking him for a divorce. If he divorces you, you are entitled to all the rights of a divorced woman, including the prompt and deferred dowry. If a legitimate Islamic marriage contract has been concluded between you, then that is the basis. However, if it was merely an engagement, then you have committed a mistake if anything impermissible occurred between you, as engagement does not permit what is forbidden. The husband's mother must cease her harm, and patience with her is a good deed, for Allah Almighty says: "Nor can goodness and evil be equal. Repel (evil) with what is better: then will he between whom and thee was hatred become as it were thy friend and intimate!" (Quran 41:34), and His saying: "But whoever pardons and makes reconciliation – his reward is due from Allah." (Quran 42:40). Honoring the husband's mother and enduring her harm is a way of honoring the husband. The husband, for his part, must restrain his mother from injustice with gentleness.