My mum died two months ago and I feel very alone. What helped you get through grief?

My mother passed away two months ago, she was 87 years old she had open heart surgery three years ago and since the surgery she wasn't feeling herself. The medications were very strong and kept her unwell most of the time. She was diagnosed with colorectal cancer in November and she died in March. She started with backache while in treatment for radiotherapy, treatment had to be suspended and the oncologist told us that her backache was due to the tumor growing and pressing towards the spine. She was referred to palliative care and two weeks after that she died unexpectedly from heart failure. We were not prepare for her to die suddenly like that, I didn't make it to be with her when she passed, which makes me feel bad because I went home just two hours before she died. When I left that evening she was very sleepy, the doctor prescribed different opioids during two weeks but never got rid of the pain completely until the doctor gave her a morphine pump and it made her feel very sleepy. I consulted the doctor about it but he didn't think much of it. The night she died the night time carer had to call the emergency services because my mum couldn't breath, she died while the doctors were there, even the doctors thought it was only an effect of the medication when she suddenly dropped her head and died, they tried to reanimated without success. I really wish I knew about signs that tells you that someone is dying, sleepiness was one of them but the doctor told me that the medication makes patients very sleepy the first three days until the system gets used to the new medication, he could have never predicted that to happen, he was very shocked about it, if he would have known he would have prepared me. Now I miss my mum a lots, she was part of my routine, I called her every night and we were together almost every day. Although I did a lots for her I still feel guilty that I didn't do enough, and that is a very irrational thought because I was with her very often, took her out shopping, hairdressers, restaurants, events, doctor's and hospital appointments but in the last six months she was very bitter and didn't want to do much. My sisters lived far away from us and only one of them came to see her Christmas and Easter, but the other one lost interest completely because they didn't have a good relationship and I felt very alone with my mum's illnesses and negativity the last year of her life. I tried my best to make her happy without success. Towards the end my sisters came to help and they were very good helping me with my mum's affairs, but I feel very alone now because I had a very strong bonding with my mum, not so much with my sisters and my dad died twenty years ago. I am happily married with two kids, but my mum has left I big void in my life. I cannot share my grieving with my sisters because they have a different outlook of life, they think it was the best for my mum at least there is no more pain and suffering. I would like to hear your experiences with grief when your loved ones died and what helped you to get through it. Thank you for reading my long post.