How do I tell my mum I was sexually abused as a child?

Hi ladies, I love eve and the community and this question has been toying on my mind lately (an understatement, it's been eating at my insides for awhile) so I figured I should come here for an opinion. TRIGGER WARNING: Sexual abuse. Ok so a little backstory (this is going to be long), when I was 5-6 I was made to perform sexual acts on other kids (by the kids, they were a few years older) and they would use threats to keep me from telling anyone. I was scared and remember feeling trapped. There weren't many kids in that town and my mother had no idea what was happening. For her sake, she had a lot going on, this all happened after we had just fled from my father and a violent home. We finally moved away from that town and I've only seen one of the kid's since. For over a decade i had convinced myself none of it happened, that it was all a dream. There was another incident a few years later where I was left in the care of my mother's ex-partners father for a few days. He made me sleep with him in bed every night. I remember being terrified. A few months ago, my family found out he had sexually abused his daughte. For years and years I had convincd myself none of this happened. A few months after i started dating my boyfriend, I told him about the "dream" and realised that I had to come to terms with the abuse and accept and heal from it. I don't know where to start, I have so many days where all I can do is cry. Lately I've been wanting to talk to my mother about it but I don't want to hurt her. Has anyone ha to do this before? how do I go about this?