pravnik is right. The rest of you are wrong (at least under U.S. law). As pravnik, traditionally in U.S. law there is no obligation to help someone in danger if you did not put them in the danger – even if you could easily help them with no skin off your nose at all. The exception to this rule is for people in a “special relationship” – once in which the bystander has some power over and responsibility for the one in trouble. The classic special relationship is between parents and children, but many other types may exist in a given case such as school official-student, minister-congregant, even doctor-patient in some circumstances. As a general rule, when someone assumes control over someone else, the controller is charged with a concommitant responsibility over the controlled.
Do husbands and wives have this type of special relationship? It’s a tough question, one that will vary from jurisdiction to jurisdiction and from case to case depending on the type of relationship the couple had. If a woman had severe emotional problems of which her husband was aware, it seems likely that a special relationship might exist as he would have already had to be her caretaker and guardian for some time. However, it is not a question that could be answered without more knowledge of the facts and the law of your specific jurisdiction.
P.S. I am not licensed in your jurisdiction, I have very little information about the facts in this case, and I do not have experience in this area of the law. I am not competent to represent you in this matter. If your question is motivated by anything more than idle curiosity, you should consult an attorney licensed in your jurisdiction, fully aware of all relevent facts, and expert in this substantive area of the law. I am none of these things. You are not my client. I am not your lawyer.