Rocmg, you wont regret how you feel now, you will look back and know- that was how you felt, but in the end you did everything possible and you are doing everything possible to look after your mum. I know I had my days where I would get very stressed out with the situation, and my mum always apologised to me - but as I told her, "I don't hate you I hate the disease - it's not your fault, it's the disease".
I have my mothers older brother who no longer speaks to me, and cousins who have told me they are happy they don't have to share my surname as it is so much easier to disregard me as family - I have NO idea why they feel this way - but I know I have nothing to feel guilty about as I did the best I possibly could to keep my mum around as long as possible. Can they say the same - definitely not! I had my doctor recently tell me what a great job I did and should not feel one ounce of guilt because I did the best I could, I and do feel that way - even with my occasional rant and rave, but I think it was more because there was nothing else I could do to make her feel better, or to stop this progression, you do feel useless as a CALS at times!
Now that mums gone, I wish I had spent more time, we will always look back on how we could have done things better, but know YOU ARE DOING YOUR BEST! Perhaps you need to speak to a third party about your feelings, as it may be they have built up and being your mums fulltime carer - she is the only one you can take it out on - my kids cop'd the worst of me! I tried to never take it out on mum, but not good for my kids.
The only things that matter is you love your mum, and your doing the best you can, even when that feels like you are beating your head against a brick wall. My thoughts are with you!