When someone you love has betrayed you, it can be hard to think clearly. Any lame lie they tell you might sound plausible. You may feel that your husband has turned your marriage into a battlefield. He has made you "the enemy." You might be afraid to talk to family and friends until you are sure. Here is how to catch him.
Check your husband's phone. Look at the call history. What numbers has he been calling? Who has called him? If you think he is sneaky enough to delete numbers from his call history, hit the redial button and see what number comes up. Or use the *69 feature to see who called him last. If he is deleting a woman's number from his history, it is because he is hiding it. He has a reason for hiding it.
Check your husband's computer. Look at history. Look at email. If you think he is smart enough to delete any incriminating evidence, purchase a key logger. It is a device that connects to the keyboard plug and then is plugged into the keyboard computer port. The logger comes with directions. The hardware is easier to use and won't be found. Software could be found. The logger will show what your husband types. It could give you the login and password to a secret email account. Or show what he typed in an instant message.
A voice activated recorder is a way to hear what your husband says on his cell phone while driving. If he's having an affair, his car is a necessary tool in his deceptions. The recorders are not expensive and one with a battery should last all day. You will have to give some thought to where to hide the recorder so he doesn't see it. Practice a few times before you try it on him to work the bugs out and make sure you don't get caught.
A GPS logger is a more expensive way to uncover your husband's betrayals and lies. There are 2 types. One is magnetic and attaches to the underside of the car. It has a battery that lasts usually 3 or 4 days. You retrieve the GPS and download it to your computer and you can compare where your husband said he was to where he actually was. There are real time GPS devices. These are more expensive and require a monthly service charge. They have to be connected to the car's battery and they can be accessed real time over the internet. Unless your husband has long term problems with fidelity (in which case, why are you with him?), the battery operated unit is fine.
Once you have "proof" of the affair and your husband cannot keep denying it, you may be able to have a discussion with him over the future of your relationship with him. Men cheat because of the way it makes them feel--young again, desirable, risk taking, exciting, etc. It has nothing to do with you. It has nothing to do with the other woman. The affair is not her fault so don't place your anger on her. Your anger should be directed at your husband. This was his choice.
Your marriage will never be the way it was. You will never feel the same again about your marriage or about your husband. It will be hard to trust him. It will be hard to forgive him. You will wonder "if the going gets tough for him again, will he cheat again or will he put the time it takes into our relationship to nurture and grow it?"
If the affair really is a one time thing for your husband and he shows real regret and puts effort and time into your relationship, it may be worth saving. If your husband has a problem...maybe he can't or won't remain faithful to anyone...he may try to blame his cheating on you. He may tell you that you don't make him feel the way he used to feel (by the way, no one is responsible for his feelings but him). He may minimize what he did--he only slept with her once--she pursued him--it doesn't mean anything--He doesn't want to talk about it, this is coming at an inconvenient time for him. If he tells you anything like this, he has more serious problems and he isn't taking responsibility for his actions. You will want to talk to a professional (both therapist and lawyer) to help sort out your options.