1.       Working a lot of overtime
your partner claims they need stay late for a meeting when they are really meeting with the lover. A big tip off that it’s not really overtime is that there will be no increase in pay on your partners check.

2.      Excessive use of the Internet
the Internet has become a dating tool for both men and women to meet others. It has become a way for people to explore their sexuality in private.

3.      Unaccountable Hours
your partner is not able to explain the reason why they have not been where they say they have been. This is the time frame to schedule surveillance.

4.      Hiding the phone bill
this is #1 way to find who the lover is.  If you partner is hiding the bill and won't let you see it, then obviously there is something on there that they don't want you to see. 

5.      Saying "It's your imagination"
Your partner might fight back with you and say "It's your imagination" when actually it's an indication that you are getting too close to finding out the TRUTH.

6.      Getting hang-up phone calls
the lover wants to speak with your spouse...maybe they had a spat.  Calling you is a way to make you aware that there is an affair going on.

7.      No longer interested in sex
as years go by, many partners experience changes in their sexual activity.  However, if your spouse completely eliminates sex from your relationship then you should consider that there is a possible affair going on.

8.      Not wearing a wedding ring
if your spouse no longer wears their wedding ring that is an indication that they want everyone to know that they are single.

9.      New sexual techniques
over the years you and your partner always had sex a particular way and now your partner comes home with new sexual moves that they learned from being with someone else.

10.  Saying "I need my space"
Perhaps your marriage is on the rocks and your partner tells you that he needs his space. This could be a way for him to move to the next stage; separation.

11. Grooming habits will change

Cheaters will be more attentive to their person (i.e. the way they dress, Cheating spouses may lose attention in the activities in the home. They don't show interest in the livelihood of you or the children that live in the home. Nor do they have any desires to do any fix-ups to the home (i.e. lawn care, house repairs, etc.....)

frequent              bathing, physical fitness, grooming of their hair, switching of colognes, etc...).

12.  Finances

Another sign is "Finances". "If someone wants to play they have to pay" therefore keeping an eye on their monies (i.e. check stubs, bank account balances, credit card bills, etc...) would tell you whether their spending more money than usual.

13.  Loss of interest in home activities