Fantastic Caregiver but disagreement about future

First off,  I do not want this post to in anyway insinuate that  my wife and primary caregiver is in anyway lacking.  She has been there for me for the past 2.5 years since diagnosis and through my several major surgeries and all of the ups and downs of treatment.  What I am struggling with is that after this length of time battling Stage IV rectal cancer and having 2 major liver resections, several ablations, 36 chemo treatments (first with folfox w/ avastin then folfiri with avastin, and 28 radiation treatments while having 5FU infused for a week at a time I feel my body is finally giving out physically.  

My cancer though still present is well controlled at the moment, as long as I am on the chemo regimen.  The main emotional issue I am having is that It is becoming very, very difficult to continue working at the high level that I am accustomed to while still maintaining my chemo regimen.  

Before I go on, I need to back up and give a little background on my wife, 10 years ago she was diagnosed with stage II breast cancer in one breast and elected to have a full mastectomy and 6 mop up chemo treatments.  I was her caregiver through her ordeal and I have to admit she was tough througout her surgeries and treatment. 

I have tried several times to discuss my physical state as well as my emotional state with her and she just keeps telling me to be positive and don't push myself so much.  Yet, in the next breath she will say that I need to get up and move more and quit acting like I am dying. (some days I think death would be better)  Other days I feel good and try to get out and do things around the house, mow grass, put by firewood, work in garden etc.  that I used to enjoy doing.  Since I have very little stamina when doing physical work, I get tired really quickly, esp. in Louisiana heat and usually have to spend most of the remainder of the day resting to recover.  In those cases she says, see you done too much.  

I am a high school principal, and that work is pretty high stress and mentally exhausting for a perfectly healthy person.  I am having more and more trouble performing at the level that I was prior to my dx and find myself missing more and more days of work due to chemo side effects.  When I miss work, I just get a look from her that says, how can you be so weak, you should have remained at work.  

I get it that she has been through the cancer dignosis and surgery and treatment, but after 6 chemo treatments, she recovered and has had no inkling of a reoccurance.  I don't know what is going on but on top of feeling physically exhausted and worn down, I am feeling very emotional about this state of affairs and I am afraid that I may have to end up on disability retirement soon.   We can make it with what I would get from retirement but I still would feel so guilty about hurting our lifestyle, which is frugal to begin with.  

Any advice on how to deal with my issues would be appreciated.  I dont know if I should try again to discuss my feelings with her or just keep on trying to put a brave face on each day and power through the pain, weakness, fatigue, nausea, etc. that comes with the chemo.

Tim