From what I see you have three problems.
1. Your low self esteem.
2. An unhappy marriage.
3. Your children are you only purpose.
Your life has value minus husband, children, and anything else you can name. God created you in his image. Have you ever taken the time to imagine the kind of life you would like to lead? Get real detailed and vivid with that image. What kind of woman do you want to be? What kind of wife? What kind of mother? What steps do you need to take to be just that?
Notice how none of these things really depend on another person.
Begin each day by looking in the mirror and saying to yourself, "I am fearfully and wonderfully made." Begin to think positively about yourself. Each day pick things about yourself you like and at the beginning of each week add another thing. Learn how to like the things about yourself you can't change (for me was my height - now I think I'm a perfect height).
Set daily goals revolving around all kinds of aspects of your life. Exercise for 10-15 minutes at the beginning of every day. Jumping jacks, push ups, jogging in place, dancing, something to get the blood flowing. This will help with your energy levels, circulation, brain chemistry, and thinking more clearly. Try new hobbies, new foods, new places, new things, new people. This will infuse a new sense of wonder and excitement into your life. You can also include your children if you like. Get them involved in different or new activities and then get to know the other parents or adults involved in that activity.
As you begin to do these things the other things will fall into place. Check out the movie FireProof. It may help too. I will keep you in my prayers.