It saddens me to read of your hurt and, as do you for it is very close to you again, right now, that this time of year can be a difficult and painful one for many.
For reasons different to your own, I find this time of year very disturbing. I don't look foward to it and am always glad when it is over. I won't go into the why's and wherefores here.
However, I do empathise with your pain and sadness. I don't wish to be trite or insincere and I cannot know the real nature of the relationship between yourself and your mother. I do know, though, that there is little as profound and resilient as the feeling of mother for child, no matter what.
For that reason and I hope you'll excuse me if it seems too personal, I urge you to put aside your doubts and worry about 'moments' in your relationship or mistakes, disagreements or whatever upsets. These are part of life for all of us. Those who care for one another let them go, as I feel your mother would certainly have done.
I know from your posts that you are someone who 'feels' and 'cares' and so I urge you to embrace your pain and sadness in tribute to your mother's memory and not to let deleterious thoughts of 'might of beens' or 'what ifs' to interfere with your grief, which is a symptom of your caring.
Please, attempt to turn away those doubts by remembering the good your mother gave to this life and the warm, funny,, beautiful and caring interactions you had with her.
Grief is important in its enabling of us to reconcile with loss but it need not be gloom & depression if we choose to focus on the positives that someone brought to our lives.
Take care. Be safe. Love yourself as much as you do those you've lost - it is what they would wish for you.