Have you ever had a sex dream starring someone other than the guy you're sharing a bed with? If so, don't worry--it doesn't mean you want to cheat. Instead, the person you're dreaming about usually signifies what's going on deep in your psyche. "If we pay attention, there may be something we can learn from our dreams," says marriage therapist Sharon Gilchrest O'Neill, author of A Short Guide to a Happy Marriage. "Maybe there's something missing in our lives, or maybe there's a problem in our relationship we haven't wanted to think about." Here are some of the most common sex dreams and what they really mean.