GreatAchiever1:
I admire the persistence but you should not leave your husband no matter what, I don't know how hard you've tried helping him overcome his gambling addiction, probably it's the kind of herd he has ganged up with that introduced him to it. I believe you should try and challenge him to become a better father(be respectable and submissive about this) and back it up with prayers. There are Men coaches online including pastors where he can listen to their messages and be motivated to take up fatherly responsibility, encourage and cheerlead him in doing this.

And for your boys, don't bad mouth their father to them. No matter what a boy when growing up needs his father even if he is not responsible(afterall they are the result of their father's seed). If your husband is lacking the father figure they need at that age, I don't know if you have relations that can teach and guide them in the right masculine path. A boy needs mentors to look up to to become a man so as not to become a nuisance in the society and a woman can't be the mentors they need. Again I will say look up resources online they can learn from incase you don't know relations that can help guide them.

Who be this guy?

She should stay and lose 2 precious humans to a man like this in the name of marriage? If she was your sister, would you give this advice?

Let's be guided, please.

She should leave the useless man and focus on raising her kids. She should ignore useless advice.