For instance, perhaps he'd always be glued to the television during football games refusing to miss a play, but now he's off in the other room with the door closed.
While it may seem counterintuitive, another sign of a cheating man is that he's overly complimentary of you.
Since you know how your man typically behaves in many situations and have clear insight into the different nuances of his personality, any deviations from this norm should be a wake-up call that he may be unfaithful.
It's even believed that men are more likely to fall in love at first sight compared to women.