UFO

There are two things I was sure would never happen, an extraterrestrial landing in our yard and my sister having a boyfriend, of the intimate kind.  My big sister is developmentally delayed, and until my mother's passing had resided in the shelter of our childhood home.  She is now a resident of an independent living facility near both my brothers (one, her legal guardian), and although I am geographically distant, I am connected to her in a way they seem to be incapable of.  In four months time she has acquired a serious boyfriend (you could knock me over with a feather), who has taken over her life in a suspiciously controlling manner, although she insists she is happy.  I don't know how to proceed and I have tried to alert my family to the potential pitfalls of this relationship.  I spend many waking hours calling my sister and her caseworker, and I am so exhausted my head hurts.