What do I do?

I will try to make this short but not sure if I can. My husband and I just married last November and have lived together since we became engaged (2 years). My husband (we) is a caregiver to his mother who is 75, had multiple strokes and has dementia (maybe earlier to mid). He was taking care of his dad also before he died last year. She has basically given up on everything, she will not walk without assistance (although she can but has issues and needs handicap assistance after a short time (rails)) we try to do all that we can for her but there is only so much that we can do. She sleeps most of the days and when she is up all she does is call for my husband or i to do things for her. He is at her becking call constantly, he (we) doesn't sleep and goes to work exhausted on a daily basis and falls asleep on the couch at 8:30 every day (keep in mind we are only 42!). He found himself in the hospital earlier this year for four days, stress and worrying are effecting his health. I had quit my job so I could take care of her in the day time, it became too much as I found myself hurting my back trying to help her out of bed and it took its toll on me. We found a great adult day care, not only to help take care of her but to also get her some mind stimulation and socialization. It helps a lot as the lady who runs it is a RN and very experienced. My MIL gives my husband the guilt treatment every now and then, he doesn't see it but I do. I spoke with the RN at the senior center and she thinks that she is manipulative and she has been nasty with her from time to time. She won't do anything for herself including walk and won't even wipe herself after she uses the rest room. All in all, this is only a little of the story.....she is not in good shape, she has fallen and we woke up to her screaming and bleeding on the bedroom floor. I understand that she is scared, but I don't think we can give her the help that she needs. My husband sees it but he refuses to believe it. We don't have a life, everything revolves around the care of my mil. I can't take it anymore, I find myself thinking about leaving....its tearing us apart. How much of life are we supposed to lose? He is depressed and a robot at times.