First of all you need to get him alone and without whining, pleading or screaming (these are how I can get when frustrated), just state that first of all you love him, you love your little family and divorce is not an option.
Tell him you two need to decide what it is you want your marriage to be. What kind of life do you want for your children.
Write it down. Get a tablet and on each page write, Today, Next week, One Month, 1 year, 3 years, 5 years, once all of the kids are in school.
Then make a plan for each of these goals (on each page). These should include personal goals, what are you and he wanting, needing, willing to do. Try to give yourselves your own deadlines.
If today your goal is to go home, get all of the laundry out of the way, both of you state what part you will take in making this happen. Who will gather all of the laundry, who will start the wash, who will move the clothes and start the next load, who will fold..
If you are determined to have sex, make the plan on who will cook the meal,who will feed the kids, who will give them the bath and who will put them to bed?.. Then who is going to change the sheets, open a bottle of wine, turn down the lights and light the candle?
Then make a plan for the next few days, then week etc... Try to reach these goals buy helping each other. Plan the meals, the laundry, the lawn care, the sex, the bill paying.. Whatever is going on. Let him know that you and he are a team and you both have goals for the family and need to help each other.
You say you are on a very tight budget with 3 small children, your husband works and you want to go to nursing school. How about getting some of that debt down and then starting nursing school? He must feel like he is a slave to his work cause he has to take care of all of the income. Let him know exactly what your plan is for paying for tuition, books, and childcare while you are in school.
How exactly is your household going to run when he is working full time and you are in nursing school and your child is in first grade with home work? It all sounds so overwhelming, and I am sure he has never seen a working family. Help him visualize this.
Then make a plan for your marriage. How are you two going to start working on your marriage? Can you guys take the kids to the park each saturday morning and have a breakfast picnic? Can you swap babysitting with another family so you can have date nights? Date nights do not have to cost a lot, think of fun and inexpensive thins to do around town.
Your marriage is worth planning and working towards. You two need to learn to be truthful with each other. You need to not freak out when he is being honest with you and he needs to really hear what your concerns and needs are. Then just try to figure out a way to work towards these goals it is the effort that really counts.
I am sending the two of you love and strength.