What are your ages?
Why do you stay with him if he treats you this way?
Do you have friends you can walk with?
Are you close with your family?
Love doesn't mean having to take care of him like he's another one of your children. You have to at some point look at the relationship and ask
You have to be honest and decide whether or not it's worth it to stay in this relationship. Maybe it's time to think about moving on if he's not willing to make any changes, especially when these changes have so much to do with getting your children back. Even when we can't make the best decisions for ourselves, we need to try and make the best decisions for our children.
As far as the exercising. You didn't gain the wight in one day, and you can't lose it in one day. Start out by walking, maybe walk from the door to the corner and back once a day, just to start out with. Talk to your doctor, ask how they can help you get on the right track. I welcome your thoughts, let me know if you want to talk more.