DEAR ABBY: My sister "Darby" and I are in our 20s and confused about the relationship she is in. She's 23 and has been dating a 22-year-old man. They fight a lot because he can't stop talking about her ex-boyfriend. He says he visualizes her having sex with him, and is frustrated with himself for not being able to get the images out of his head. Is there a name for this particular problem, and how can Darby work with it? -- SUPPORTIVE SIS IN THE WEST
DEAR SIS: Yes, actually, there are two names for this "condition." They are obsession and jealousy, and both are signs of potential control issues. Stay close to your sister and be there for her, because this young man's behavior is a red flag.
Darby and her boyfriend are both adults. I assume neither came to the relationship wrapped in cellophane. His fixation should not be hers (or yours) to fix. Because he can't get the images out of his head, he should schedule a few sessions with a licensed psychotherapist, since his problem will continue the longer he is in the dating world.