I will be blunt with you. First, I'm glad you came on here and were honest. Usually people want to "put up that front" of being the perfect person and saint, when inside they are tearing themselves to bits. So I want to give you some kuddos just for coming here and being honest when it wasn't "pretty."
Second, you are a living, breathing human being and until the day you die you will have emotional and physical needs too. I admire you for wanting to be faithful to your wife especially now in her time of need, but guess what? Just because she has physical illness and limitations doesn't mean that your needs suddenly stop. Let me pick one as an example: the need for Admiration. Often fellas like to hear a little appreciation when they do something right--their woman gushing all over them thanking them for leaving the cave and killing the dinosaur for example.
in your instance I bet it would do your heart a world of good to hear your wife say, "Honey I know you have given up a lot to take care of me and keep me company, and I know you get very little sleep all because of me. Thank you so much for your constant love and tender care. It means so much to me that it's you and not some stranger caring for me." Am I right?
So you're wife may be ill, and let's be honest here DotComDaddyO, we are ALL dying so that's nothing unique! The fact is, she is not dead yet and while she is alive she has the duty to do her very best to meet your needs. Yep she probably can not mow the back yard....but she sure as shooting could say thank you! Or express love or affection!
You've gone a long time being the Giver in your marriage and now your Taker is starting to rear his head...and with good reason. I would suggest going to my website (there's a link in my siggy if you want to take a peek) and learn about Love Kindlers and Love Extinguishers. Right now you do love your wife, but you are vulnerable because for a long time she has not been doing the love kindlers she could do (and I realize they're limited but still) and she is engaging in love extinguishers. Since this situation could literally go on for years, it is just not reasonable to expect you to give all, her give none (or extremely little) and have you stay. Period. Even the most committed person would eventually leave if only for a break!
Your marriage is where it is now and it may stay that way. I suggest that you find ways to fit in YOUR needs into this marriage too. For example (just brainstorming here): you NEED to get sleep! That can not continue for the long term so arrange for someone to be the responder overnight during the week and on the 3 weekend nights you can do the overnights and nap (sort of like new moms do with an infant on a 24-hour schedule). The fact of the matte ris that without sleep it will harm YOUR physical health, mental health, emotional health, etc.! This one is imperative even if she fusses about it. Next I'd say arrange to have some time to yourself with friends--like go out to dinner with a small group or join a bible study. For your own mental health you need to have some interaction with other adults who can also support/encourage you. Finally I'd say you have a talk with your wife and let her know that you are not backing away from caring for her but that all this care has been neglecting you, and that isn't healthy either. You can not care for HER if you do not care for YOU. So you need to reach an agreement together to meet some of your needs too--and yeah that specifically means that she would do what limited bit she can to meet your needs. This isn't being selfish--it is being reasonable and realistic. So yeah--ask her right out if she could say "thank you" every now and then or a heart felt "I love you". Shoot maybe just be honest and tell you that she is so mad at herself for being dependent like this!
Long story short, you aren't being a jerk to expect/want to have some of your needs met too. That is normal and reasonable. Now go ahead and work on getting them met within moral boundaries, of course.