Oh Jen, what a tough position for you to be in. In some states, what he did is actually against the law, and criminal charges coukd be brought against him. There are a bunch of links at the top of the page for those abused by therapists. Contact TELL by emailing- they can help you look at the options.

It sounds as if you understand that your sister has no blame in this. She has been manipulated, and her need to keep his secret is part of that. Kind of like a sex abuser who tells a child his mother will die if he tells - she is afraid she will lose him if you tell.