My darling Mother was diagnosed with Alzheimer's in the summer of 2013, and I'm caring for Mum 24/7 and I'm so glad to be the one since we've always been very close, and good together. All's going well so far, but I know that there are tough challenges ahead for Both of Us. Mum is 86 years now, and I'm 55. Thank You All for Your contributions, and help, as this site is My road map through this awful condition.
https://www.agingcare.com/Alzheimers-Dementia
I do know of someone who cared for her husband with ALZ from diagnosis until death, but she also was a full time homemaker, had help during the last years, and definitely wanted to do it.
I think the challenges that make you question your decision might come at the stages of hostility and complete immobility.
What you can do is learn as much as you can about the condition and its stages, make short and long term plans, including how you will cope with changes and what help is available to assist you during those changing periods.
Develop alternate and fall back options for each stage. Identify situations that you think and/or know you can handle, and those which you are sure you couldn't handle, and again, develop options for those stages.
I would also contact the local chapter of the ALZ Assn. and ask if they hold the Creating Confident Caregiver's Course. http://www.alz.org/mglc/in_my_community_58958.asp.
I took this free course, which deals with ancillary issues that affect elders who don't necessarily have either dementia or ALZ. It's definitely worth it and will give you a lot of insight into dealing with ALZ.