Dear Amy: I am a 72-year-old (divorced) man. Four years ago, I met my widowed girlfriend (age, 70). After dating for over a year, she asked me to move in and live with her in her spacious house, where her sister (age, 64) also lives. "Sister" suffers from severe clinical depression, and is on medication and medical care. I accepted my girlfriend's invitation after receiving assurances from Sister that she is OK with this plan. When Sister doesn't get her way, there is hell to pay.