I have a somewhat different opinion. My husband has "joked" with me many, many times that I am cheating on him. Or that I will leave him for someone else. All of his fears were unfounded.
This has always stemmed from his own insecurities in the relationship. I know the baggage he is working with, so I try not to let it get to me, but there are times when it gets really, really old. We've been together almost 10 years, married for almost 2.
I'm not saying that gut feelings don't have validity - quite the opposite in most cases, but thinking doesn't always mean it's true.... My 2 cents