I do understand what you are going through, My husband has a GBM dx 11/06. Until last summer he was "normal" but the cognitive, physical and emotional changes since last summer have been so difficult to deal with. I hate when people tell me, "Be patient, he can't help it. You know it's not the real him." I know all that, but it does not make it easier to deal with. This web-site has helped me a lot.
There should be a social worker at the hospital where your husband is treated who can help you in many ways.
I have found the social worker a wonderful person to talk to, someone I can vent to and has been able to give me some coping strategies.
The social worker will also be able to help you find ways to get some help with your husband. Check you health insurance and see how much they cover for Hospice and for home health care. Our social worker did all the leg work to have my husband admitted to hospice-all I had to do was take the phone call from Hospice to set up a time for them to visit.
Hospice today is not what it used to be. There are many, many services available for the patient, but also the caregiver-one of them being respite care. My husband is doing fine right now-not dying any time soon, but he is only doing palliative care now so he qualifies for hospice.
There may also be volunteers in your community who will come and stay with your husband so you can get out. Look into adult day care programs as well. Not sure where you live, but see if there is a "Senior Helpers" in your area. My friend owns the company in MD and they have franchises all around the country. They send people out to help those who can't get out on their own or just need some help at home--sort of like babysitters for adults.
And yes, mnay of these things cost $$ and that may stand in your way of using them. So if family members say they want to help but can't b/c they live too far away, tell thme they can help by paying for some of these servies, if that is the kind of help you can use right now.