My top pick for tips on how to catch cheating is this book by Sarah Paul

Seven Signs That He Is Cheating

After a while you will notice subtle and not so subtle differences in the behavior of your husband or boyfriend. Before you jump to conclusions and start hurling accusations at him, calm down and start looking for signs that he is cheating. He may be very careful and be able to cover up and offer plausible explanations and alibis, but sooner or later he will slip up. You do have to become really observant of the little things that you would never have noticed before your suspicions were aroused. Apart from the obvious signs of lipstick on the collar, the scent of a different perfume on the clothing, some of the top signs include:

1. Your man starts spending less and less time at home and does not seem to have the same interest in the two of you doing things together. It will seem as if every time you suggest an outing, such as going to a movie or out to dinner, he has an excuse of why he cannot go at this time. He may start working longer hours but you notice that his pay hasn’t increased with all the overtime. There may be more evening meetings than usual and always at expensive restaurants.

2. You notice a significant decrease in your sexual lives or maybe it has become nonexistent. This is the prefect opportunity to ask what is happening because the reasons may be medical. If he comes up with excuses of being tired and not in the mood all the time, then you can take it as a warning sign that there is another woman in his life.

3. He starts taking a more active interest in his appearance, buying new clothes, working out and changing his hair color. This is especially significant if he doesn’t discuss any of the changes he is making in his life with you.

4. If you have to adjust the passenger seat of the car on a regular basis to suit your needs, you should ask who has been sitting in that seat. It could mean that the woman he is seeing is taller or shorter than you, which explains the change of position.

5. Guilt often comes into play when a man is cheating on his partner. He starts bringing home little gifts or sending flowers, which is really out of character.

6. Charges appearing on the bank statement or credit card statement for purchases, hotel accommodations or dinners in restaurants that you don’t know anything about are also signs that you can’t ignore. Not only are you paying for his dalliances with someone else, but it shows that he is really trying to let you know that there is someone else in his life.

7. A cheating man will get very defensive when you question him about his whereabouts and often will become angry. If he doesn’t have anything to hide, it won’t be a big deal when you ask him about it. Just be careful not to do in an accusatory tone to set off his alarm bells.