Observe the behavior of the husband
Often the woman is unaware of infidelity, because he doesn't want to see her. Try to impartially evaluate the behavior of the husband. You should alert sudden mood swings, the long hours at work, frequently changing plans. Remember, maybe your spouse often called to work in the evening or on weekends. It's a red flag. You can to check on her husband, calling him to the office and learned about his schedule. If the husband has a mistress, he will try more often to absent himself from the house. The pretext will be the help his brother, fishing with friends, lunch with my parents. If such absences become too much a reason to think. Also the husband can change his behavior towards you. He can be extremely affectionate and caring out of a sense of guilt or, on the contrary, he will ignore you and get annoyed for any reason.
A sign of a relationship on the side is a sharp change in sexual habits in any direction.
Of course, to delve into other people's phones and computers - not very good. But sometimes it's the only way to prove adultery is not. If your moral principles do not allow me to check the contacts of her husband, wait for the right moment. Sooner or later, he can leave the phone open messages or call log, or forget to log out from your account in the social network. You can also go to the trick - ask the husband to give the phone to make a call, supposedly you run out of money. Or say that you need to send the email, and you forgot the password of my email. If the spouse will become confused or begin frantically to remove something from the phone and mail, ask directly what he's trying to hide.
A sign of trouble is sudden "secret" conversations of a husband behind closed doors and often sitting in social networks.
Image change - proof of infidelity
Rare man following the fashion trends and are overly concerned about their appearance. If your husband suddenly became a different dress, changed my hairstyle and started to use expensive perfume, when earlier he could not stand, it should alert you. A sign of infidelity may be increased interest in personal fitness, sports. Please note, the form in which the husband goes to his overtime work or meeting friends, not if he pays excessive attention to appearance. Try gently to talk with her husband, to know what such changes are connected. But don't push it and don't make a scandal. He is probably doing it just to please you.