This is not a decision you have to rush. I’m not against disclosure of abuse, obviously, but I feel very strongly that anyone who prepares to do this needs to fully understand the potential ramifications. It’s all too easy to envision the perfect disclosure, the weepy, apologetic mother, the hugs and validation you long for. The reality is often much messier and much more cruel, and I wouldn’t want anyone in this kind of situation to face something like this without a solid, unequivocal support system in place, to be at your side regardless of how Mom chooses to react. Given her track record I think you know better than any of us what the outcome is likely to be. If you are of two minds, give yourself time, eventually the right course of action will become clear.