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.
If what you mentioned about your husband is really true, then he is disobedient to his Lord and negligent of the rights of his wife. Gambling is one of the evil matters which the Quran warned us against; Allaah Says (what means): {O you who have believed, indeed, intoxicants, gambling, [sacrificing on] stone altars [to other than Allaah], and divining arrows are but defilement from the work of Satan, so avoid it that you may be successful.}[Quran 55:90]
Also, spying is forbidden according to the very text of the Quran, and accusing someone of being unfaithful without having any evidence is prohibited; the prohibition is even more confirmed about such acts if one commits them against his own wife. Allaah Says (what means): {O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy or backbite each other. Would one of you like to eat the flesh of his brother when dead? You would detest it. And fear Allaah; indeed, Allaah is Accepting of repentance and Merciful.}[Quran 49:12]
Besides, if the husband is negligent regarding spending on his wife and his children, then this is a flagrant sin. ‘Abdullaah Ibn ‘Amr narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: “It is enough a sin for a person not to provide means of sustenance to those whom he is obliged to support.” [Ahmad and Abu Daawood]
Moreover, if the husband is dissolute and harms his wife, then this is a sound reason for her to ask him for divorce, but she is not obliged to do so. It is more appropriate that she first advises him and tries to reconcile with him, and if this is not achieved, then it is better for her to separate [i.e. ask for divorce] from him as it is not good to have a marital relationship with such a husband.
Furthermore, it is not an obligation to obey your parents when they are preventing you from separating from your husband; obedience to parents is only an obligation in what is permissible. No doubt, what harms the children is not permissible at all. For more benefit on the limits of obedience to parents, please refer to Fatwa 84942
Finally, we draw your attention to the following matters:
1. The intervention of the family of the husband or the family of the wife should be in order to reconcile between the two and not to be biased towards one party and put pressure on him/her.
2. If the husband is financially stingy towards his wife, it becomes permissible for her to take from his money what would suffice her and her children according to reasonable terms as confirmed in the authentic Sunnah. For more benefit, please refer to Fatwa 165373.
3. If all the husband's money is ill-gotten, it is forbidden to eat from it except in case of dire necessity and only to the extent of one’s necessity [i.e. if the necessity does no longer exist, the wife should stop eating from it]. If the husband’s money is a mixture of what is lawful and what is unlawful, then it is not forbidden to eat from it but it is disliked. For more benefit, please refer to Fataawa 81560 and 87211.
4. The mere separation between the husband and the wife is not considered as divorce as we clarified in Fatwa 82214.
Allaah Knows best.