Probably that you're at least a little insecure in your relationship with him perhaps?
It could be that you are being haunted. Could you have cheated or wanted to?
Unless he's actually doing it, either you're insecure or you're thinking of cheating on him and expect him to do the same in return.
It means you have contemplated cheating but you are projecting it off on him.
Unless you have reasons to think he's unfaithful, it probably means you're paranoid or have a fear of losing him.