How to greif over someone in this situation?

I've struggled with anxiety my whole life. And my mum was a huge part of my childhood. She did everything to make sure I was okay! Ever since I was a kid she was the most comforting thing in my life.

In lockdown my parents start arguing alot. long story short after lockdown they were no longer together, i still lived with my mum and we became alot closer, I have memories of her saying how proud of me she was helping her and looking after my little brother and she would call me the new man of the house. Our relationship was like a best friendship, I would *** her when I'm in class, we share the same music taste and everything was perfect!

Then December 2021 came around my mum was talking to someone new, I didn't want her to get a new boyfriend but I was supportive, I wanted her to be happy! Long story short this man was not a nice man. I got left home alone for weeks at time. A few weeks later I left my house to go and meet a friend, it turns out a social worker was coming but no one ever told me. I was about 20 minutes away and could not make it. My mum text me ( it was definitely her boyfriend on her phone) would you said it was not allowed to come home ever again.

I slept at a friend's house and coincidentally had a meeting with a social worker the next day and they put me with my dad, I've lived here for 3 years and not seen my mum since

My mum passed away in July 2024, I had 1 phone call with her four days before she died, we text that day too, she told me she missed me and she's sorry she made the wrong decisions, that she was trying to escape her boyfriend. For the first time in years I was excited to see my mum again. 4 days later she died because of heart disease. Her boyfriend never told me I found out through my mum's American friends ( who is still incredibly supportive to this day)

Me my dad had to go to court to get my little brother back from her boyfriend, he eventually lost, he was rude to the judge and he had no parental authority over my little brother.

It's just all a mess. How I grieve over someone I haven't seen for so long? If you like she's only a tiny memory in my brain ,but at the same time such a big part of my life.