It is so heartbreaking! Not knowing why is so hard, and it can lead to so much shame and guilt. When it is sudden and they cut off other people in their lives, I suspect there may be mental illness, or at least some kind of mental break. I know this has caused you a great deal of pain. I pray for a resolution and a reconciliation, and if not that, then peace and healing for you.
Wishing nothing but the best for you. ♥