Oh, hon, I know how horrible of a feeling that is when your husband checks out. The stresses of life don't leave much room for the comforts of a relationship. Can I ask you if your husband is a practicing Christian?
I can't even begin to imagine how hard it must be having 6 children. My husband is in the Army, though, so I understand alll about having to do everything yourself, not having your husband around, and having him completely stressed out by work. The best thing you can do is take a deep breathe when you are frustrated, especially with your children. Secondly, if you can't get a large chunk of alone time with your husband, try taking smaller breaks. When he gets home from work, send your children to do a chore for a few minutes, even if it's holding a little one if you have them. Greet your husband with a hug, and a kiss, help him unwind from work with a ready glass of his favourite drink and maybe a small shoulder massage. Ask him how his day went. You'd be suprised how much those small actions will mean to him, and it only takes 3-5 minutes.
Also, if you are both able and willing, try going to church together on Sundays. God gave us the sabbath so we could escape the stresses of life and focus on relaxing and relationships. Pack a lunch and take the kids to the park afterwords to let them play and burn off some energy why you and your husband enjoy half an hour or two sitting, eating lunch, and talking to each other (try not to talk about bills, things your kids aren't doing, or any other stressfull stuff). I love Sunday morning because I know I get a full hour at church with my husband next to me, holding my hand, no cell phones, no laptops, no pagers, no talk about bills or responsibilities. Just a full hour of whispering I love you and hearing the Lord's word. It's amazing.
Lastly, look to the Bible and to prayer. Make it a family event if you want. It'll keep your kids active and entertained, give you a chance to unwind, and give you and your husband and children a chance to grow. My favourite thing to read is the "lillies in the valley" story where Jesus tells us not to worry, that every little sparrow is taken care of by God, and are we not worth more than a sparrow, where the lillies in the field never work a day in their life and never has anyone seen anything clothed as beautifully as them. There are lots of good psalms to read, too.
Being a wife is hard, especially with 6 children and a husband who is so stressed out he doesn't want ot be involved. It's our job to stand behind our man, supporting him, helping him, and caring for him. Like I said, just little small things like having a drink (not necessarily alcoholic by any means) and a kiss waiting for him when he gets home will put more affection back into your marriage than you can imagine. And please, don't forget God, he'll never give you more than you can handle. My prayers are with you, and I hope some of this helps.