What should you do if you believe your spouse is having an affair with a coworker?
If you have a gut feeling something is going on, just keep your eyes open . Ssometimes the cheater loves to talk about the other even to their spouse. Signs can be coming home late, car seat in different place, he likes to argue over nothing, seems distant to you. These can all be signs that he would rather be at work with her. Is he in a hurry to go to work and have you noticed he makes sure he looks extra nice. This may sound silly but smell him when he comes home; he may have she smell on him.
Its understandable that you suspect your partner may be cheating on you but you can not wrongfully accuse them without proof. That could Jeopardize your relationship if something isn't going on. Like the other answer look for signs, does he act differently when he comes home than before? Does he seem less happy to interact with you? Is he hurrying to go to work? If all these signs are answered with: Yes, then there MAY be a problem. Talk to him. Start with: "Hows work? Anything new happening?" Then without giving yourself away start saying how special he is to you. How he is the only one you have ever loved etc. If he doesn't respond, responds less enthusiastically, then you may want to go to work with him one day, bring him lunch or something. Have a look whats going on and ask some people from his work.
Answer2: You don't state the reasons for your suspicions, but for your own peace of mind there are things you can do. Approach the matter with your mate in a very calm, dignified non confrontational manner. Be open, honest, upfront and talk about your suspicions and ask. Let your spouse know that you are not necessarily suspicious, but explain why you feel uneasy and suspect an affair. Talk it out and if your mate does or does not confess, you have options to stay or leave. (see 3/1/05 Watchtower article, Marriage Can Succeed in Today's World on Jehovah's Witnesses official website)