Calling on friends or relatives is a really good idea. I remember when a friend of mine was caring for her Mother-in-law who had lung cancer - I went over once or twice just to sit with her MIL so that she and her husband could go out for an hour or so to take care of errands or just for a change of scenery. It does help. Sometimes people don't think to offer to come to stay with the patient, but if they ask what they can do to help, you could mention it or even if they don't ask, you could mention it anyway. It's a very loving, but tough and demanding job you are doing and you do need a break to take care of yourself, too.