My brother in law is cheating on my sister with men. He has an on-line profile and uses on-line gay apps to find s**. I have anonymously been speaking to him via the app. He doesn’t know its me. This has been going on for 4 years. I really want to tell my sister but worry it will destroy her family. She is totally clueless about whats been happening. I have all his photos (some naked) saved on line for safe keeping just in case i need to use them in the future.