My issue is that I fantasize about sleeping with my best friend’s sister — I have for several years now. I feel I’m a little obsessed about her. She has a boyfriend. The worst part: we share a flat together. Fortunately, she’s out a lot, and when she is around I do try to avoid her. Do you think my desires toward her are unhealthy? Are they just a result of proximity? I currently don’t have a girlfriend but even when I did, I thought about her. It’s a tough situation and I’m not sure what to do, if anything?