I remember reading one, a long time ago,but I just can't remember the title.
Alt-Clark in our universe and sleep with Lois, while Clark is in the Alt-universe and sleep with Alt-Lois. When they are all back in their respective worlds, everybody is ashamed of what happened but they all confess, and since that made them all sure that they are with their real soul mate and that the alt-soul mate isn't The One, everything's fine.
I hope someone will be able to recognize it and say the title. I can't remember it.
