It's one of my favourite movies and for a romantic comedy, it's pretty amazing. I think Bill Murray is an excellent and uncoventional leading man. In Groundhog Day, Bill lives the same day over and over again.
If you were in Groundhog Day, and in a relationship, is it cheating to sleep with someone else?
I think it goes to show how much time relates to our morality. If we live without consequences, then how do we distinguish between right and wrong? Further, cheating relates to being in a relationship with someone and sleeping with someone else while you were in that relationship. If you are in a situation like Groundhog Day though, I'm not so sure if it would be. Even though it appears like he is stuck in one moment, I actually think it is more like the expression of the timeless nature of the universe. He is stuck in an eternal moment, where all the possible consequences of our actions play out. He is the sum of all of those different expressions, he is always the same. So really, it's impossible to say if it is or it isn't.
Or, looking at it another way, in our 'normal' time, it is possible to love and sleep with more than one person, as long as they are separated by time. In Groundhog Day, each day is a different experience of time.