He Becomes Mr. Critical
If your normally docile and easy-going husband has recently turned into Mr. Critical, it's often his way of dealing with the guilt or his affair and/or comparing you to the other woman. Many men look for faults in you in order to justify the affair and soothe their consciences over cheating.
He Begins Spending More Time Away from Home
If your husband has suddenly started working extra hours, joined a gym without the sweaty results, or taken a sudden interest in a previously unmentioned hobby that keeps him away from home several nights a week, it could be a sign that he's spending that time with someone else.
He Goes "Off the Grid" Sometimes
We live in a day and age of constant connectivity. Between mobile phones, computers, and other technological wonders, no one is ever out of touch for long. They especially aren't out of touch with any degree of regularity. If he's going off grid on a regular basis, then it's likely intentional rather than accidental and that can be a sign of real trouble for your relationship.
His Sexual Preferences Change
Sometimes this presents itself in a sexual drought at home. Other times it presents as more frequent sex than ever before. It's almost as if he's trying to make up for his indiscretion by behaving even more lovingly at home. However, it almost always results in changing preferences and evolving interests in the bedroom.
He Brings Up a Specific Other Woman in Conversation Often
If he's talking about another woman a great deal it's because she's on his mind. That, in and of itself, is cause for concern -- but not necessarily alarm. In many cases, he's thinking about an affair when he's talking about her. When he suddenly stops talking about her is when you should be alarmed.
Knowing what's going on his mind is half the battle. It is possible to stop an affair before it gets started or becomes too serious if you are aware of the signals and make a concerted effort to stop things before they really heat up.