Infidelity occurs in an alarmingly high number of marriages. There's no need to stalk your wife from the moment you're married and spend your every waking moment trying to make sure that she's not cheating on you, but you also shouldn't blindfold yourself to the possibility that she may be one of the many unfaithful spouses out there. Don't hijack your wife's privacy with hidden cameras or tape recorders and don't harass her about every piece of her life spent away from you, but do watch out for certain signs.
TIP: Read the guide to prevent a break up or get back with your ex.
Your daily interactions and communications can be signs that your wife is unfaithful. In a healthy relationship, there is a degree of intimacy to even the most basic dialogue, but sometimes if infidelity is present the offending partner may be letting romance with their spouse fade, which can show itself in simple conversations. If you find that the amount of silly small talk and playful back and forth with your wife has diminished somewhat since you were first married, then it may be because she is withdrawing herself and granting the flirtatious aspects of her personality to someone else rather than you. It's natural for marriages to develop their “serious” side over the years, as various real world issues will inevitably arise, but love should never consist of a couple of roommates; love should be between lovers, and if she's not talking to you in a way that would indicate that she sees you as one, then there may be a problem.
Another sign that your wife may be being unfaithful is the deflection of routine questions that should really be answered with ease. Things like “Where have you been?” and “What took you so long?” are not really offensive or dangerous questions to anybody who has anything to hide. She should simply answer the question, with a reasonable amount of detail, and a normal spousal conversation should ensue. If you find her repeating the question back to you, which is a tell tale sign of people trying to think of a good answer as they buy time, then you should probably be a bit suspicious. Also if she gets defensive at all in the face of these types of whereabouts questions, by saying something like “Why does it matter?” or the like, this could be a bad sign as well. It should be noted that some women might get defensive anyway, some may have already developed the habit of repeating questions before answering them, and some are extremely good at making their lies sound perfectly natural; you'll have to break out your inner detective to really determine if something is wrong.
If towards the beginning of your relationship your wife wasn't always thrilled with you opting to spend time with your friends or enjoying “me time” watching television or messing around on the computer rather than spending time with her, then she would probably still feel the same way if she was as invested in the relationship as she was when things started off. So if you're suddenly finding it a lot easier to go golfing whenever you want or to play hours on hours of video games without hearing any complaints, this could mean that she's stopped caring as much.
You may notice a decrease in the frequency of sex in your marriage if your wife has been being unfaithful as well. It's not uncommon for long term relationships to go through periodic “dry spells” where intimate time in the bedroom takes a back seat to other priorities, such as work and family, but in a healthy relationship the sexual spark usually has a way of bouncing back; if it doesn't, then there may be a reason. On the same token, if your wife is still regularly having sex with you but just doesn't seem as enthusiastic about it as she used to then this may also be a sign of possible infidelity. It's generally a bad thing if it seems like decisions about when to have sex are more centered around when your wife is in the mood and less about mutual arousal. Don't take this kind of thing as a monstrous blow to your ego though; people find the “wrongness” of affairs to give them something exciting. It often times has very little to do with actual sexual ability or physical attraction.
A fairly obvious sign to look for is the missing wedding ring. There are a myriad of excuses available for not having one's wedding ring at any given moment but in reality if you notice it more than once then it probably means that your wife is opting against wearing it, and outside of a broken finger infidelity is really about the only logical reason why she would be doing this. One thing you might want to try, whether or not you've caught your wife without her ring, is going a day without your wedding ring just to see what kind of reaction you get. If your wife never once brings it up this could mean that she's trying not to draw attention to any possibility of infidelity since she herself is actually being unfaithful. She might bring it up even if she is cheating but she'll almost certainly bring it up if she's fully committed, so it's an experiment worth trying.
Don't let unreasonable insecurity mar your marriage. When your relationship feels as beautiful and perfect as it did during the days of courtship, then it probably still is. You should always allow trust to be the most obvious solution to any suspicions that may arise. With that said though; people change and life sometimes moves in directions which we just don't want it to. So be aware of the signals that your wife is giving off and if too many things seem to be adding up against her, then make the confrontation happen and demand the truth, which you definitely deserve.