my 8 year old keeps stealing food
Does he hoard the food, that is hide it? Is he hungry? Are there snacks out that he can eat? Can he help himself to fruit, or milk and crackers, if he appropriately eats this and cleans up after himself? Does he ask for food and is he denied it?
How is it that an 8 year old would be considered to be stealing food in his own home? Does somebody own the food? Is it not freely his, too?
Why would your husband threaten to leave you over this? Do you want a husband like this?
Are there other marital issues that your son sees or senses? Could he be maybe reacting to those?
You seem fearful your husband will leave you. Maybe that is what needs to be faced, before you can help your son. You may need to confront your own situation.
Your child is helpless without you. He is defenseless. If you feel unable to care for him or you feel your marriage is your priority perhaps that needs to be faced first.
Your son may have unmet needs, much beyond the craving and needing of food. He may need something from you, his mother.
I believe you need to make a decision about where you stand. Your son needs you.