I agree with Geoff.
I wish I could offer more helpful words.
I know it is hard to see now but I think that what you did last Friday brought the abuse out into the light. And that is always the right thing to do. I don't think it is ever easy. I do think you will help your sister to receive healing herself now that is out in the open. Maybe you could focus on being there for her now as I'm sure this will affect her in some way. You have been there for us and I know you have the understanding of abuse to support her recovery.
Also you can't be expected as the younger brother to have protected her - so try not to beat yourself up about that. Sounds like you have a good therapist. It is great that she has the resources to get you in a respite home. Surely this will help you to clear your head and work out were to go from here.
We are all here for you mate!
More than meets the eye!