Reading through your question, it sounds like you are working pretty hard to take care of your wife right now, and this is not going to get easier with a
disease like multiple sclerosis. The amount of lifting and other physical care you do certainly takes a toll on you, physically as well as mentally.
You should not expect yourself to care for your wife alone forever. One of these days, you are going to get burned out or hurt yourself, as caregiving is a tough job! What I would recommend is getting in touch with a social worker from the Department of Aging in your area. They can help get you in touch with services that are available in your area that can help. Furthermore, they can help assess your current situation and offer you guidance about the next steps in taking care of your wife. They will let you know if a nursing home or home care is appropriate for you.
Your last question was about the life expectancy of someone with MS (multiple sclerosis). Unfortunately, it really depends on the person, so I cannot really give you facts or figures. The disease will progress, so soon, she may not be able to tolerate getting up out of bed at all. This will open her up to other problems, like pneumonia, skin issues, and urinary tract infections.
Sometimes, joining a MS support group, where you can share experiences and feelings with other people who have similar situations, can be very helpful. Ask your wife's neurologist if any MS support groups are available in your area.