My husband wants to move away from my mother, but she needs my help; What should I do?

My mom is 81, she lives a few blocks away from me. I am married now 17 years with a 10 year old daughter. my husband wants to move. I have tremendous guilt about this situation. he says we move or he leaves. No one knows why he would walk away from a marriage over 17 years based on where we have lived all these years. (note: we live in a home my mother gave me, as he was bankrupt and lost his home when we met). I help my mother all the time, we help each other. I cant move , I cant. I feel crippled by having to make this choice. what should I do.