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

How to Spot the Signs That Your Boyfriend Is Cheating

If you have a suspicion that your boyfriend is cheating because of the changes you feel in your relationship, you are probably right. Trust your woman’s intuition because your gut instinct is almost always right. Before you do anything rash, like confront him about it or call a private detective to have him followed, look for the signs that your boyfriend is cheating.

These signs include some of the following:

* A lowered desire to make love when you are in the mood
* A sudden desire to try new positions, which is something he never wanted
* A tendency to work later hours than usual
* Receiving mysterious phone calls that he takes in another room or passes off as a wrong number
* Won’t allow you to use his cell phone
* Gets mad if you check to see who is calling when his pager goes off
* You get the scent of a different perfume off his clothing
* He takes a shower as soon as he gets home, which is something that he never did before
* You find a phone number in his pocket
* He makes sudden changes to his normal routine
* He starts accusing you of cheating on him

Just one of these things does not amount to cheating. Your boyfriend may change his routine or start taking more care with his appearance to please you. This is also true of trying to lose weight or starting to work out at the gym. What you do need to look for is a combination of these signs.

Start a casual conversation about someone you know who has just found out her boyfriend is cheating on her. His reaction will tell you something of your relationship. If he seems uncomfortable talking about this topic and wants to change the subject and you have a gut feeling that he is cheating, you may be right in your suspicions. He may become really irritated with you when you persist in keeping the conversation going.

You should not confront him and accuse him of cheating without the evidence to back it up. This will do just as much harm to your relationship as the actual cheating does. You could ask about certain things you have noticed just to see what his explanations are. They may be legitimate and when he realizes your fears about your relationship, he may become very apologetic and resolve to do better in the future.

If you don’t have the evidence to support your accusations, you will not get the answers you want - which is the truth. He will be able to make up excuses just to keep stringing you along. At the same time, if he wants out of the relationship, he may admit to cheating right away.

Short of following your boyfriend around to see where he is going, you do need to be able to recognize the signs and then decide how you want to handle the situation.