A few weeks ago my girlfriend Deb called me on a Sunday evening. Sunday evenings can be bleak when you’re single and don’t have kids — it’s the time of the week when one can feel most adrift. And winter is upon us — it’s dark by five these days and we’re all living with a tiny bit of dread knowing that the wind will start up again. “Why don’t we do dinner a couple of times a month?” Debbie suggested. “We could get single people together, and rotate it to different houses.” So last night, we did. There were…