I left home when I was sixteen and my mom was never the motherly affectionate type. Mom has always been somewhat moody and suffered depression (even though years ago it was talked about). Anyway as the 3rd child and 3rd daughter I can't say I was ever very close to my mom and definitely grew distant from her over the past 40 years.
Now my mom has outlived 3 of her children which leaves just me and my older sister. I am the one that lives close to her so it has fallen to me to take care of mom.
The odd thing is that now that I am in this situation I seem to be growing closer to my mom, more understanding of my mom (even though I sometimes want to wring her neck) and I am learning a new level of patience.
I have heard the phrase "Everything happens for a reason" and I am believing this is true. I was put into my moms life for a reason we have and are learning and growing through each other.
Some people would view the situation as a test you are passing (or that your mother is passing) and you are being rewarded. Some people would look at it as building good karma for the future, or using karma from the past. Some people believe that this is part of God's plan for you. The belief that really matters in this case is yours. However you find meaning on a philosophical/spiritual level is your truth.
Once my sister-in-law said to me that God did not give the caregiving burden to people who can't handle it. I replied, "Oh my gosh! My poor husband should have married someone else! If only we'd known ..." She was startled and assured me I was the perfect wife for him. "But," I explained, "from what you just said God wouldn't have given him dementia if he weren't married to a strong person who could handle it!" Obviously my SIL and I have very different life views. That is OK, we get along fine and want only the best for each other. Whatever your views are, some people share them and others do not. Doesn't matter.
Of course you sometimes want to wring Mom's neck -- I'd think you weren't paying attention to her if that didn't happen. But good for you for learning patience and tolerance.
Whatever your belief system, embrace this opportunity for learning and growing. However you explain it, it is happening at a time you are receptive to growth.
Grasp ever positive from this challenging situation that you can. Hugs and best wishes to you both.