If you want to know if your wife or girlfriend is cheating on you, there are many tell-tale signs you can look out for. Of course, the only sure way to tell she's cheating is with a confession or hard evidence, but looking out for these signs can tell you if you should start worrying.
Watch to see if she has a sudden and drastic change in her routine. If you and your wife have always gone to lunch on Friday afternoons, and she's always gotten together with her girlfriends on Wednesday night, but she suddenly starts making excuses why she can't attend those things, she might be hiding something. A cheating woman will alter her schedule to accommodate meeting with her new lover, no matter what.
Notice if she becomes overly sensitive and secretive. A woman who is hiding something starts to live her life as though everything is a secret. She may freak out if you look in her purse (even though there's no evidence in there), and will get defensive at the most benign question.
Be on alert if she suddenly becomes argumentative. If your wife starts lashing out at you and picking fights over any little thing, whereas before you had never argued, it could be because she's stressed about all the lying and hiding she's having to do lately. This is especially tell-tale if she starts picking fights so that she can storm out of the house in a huff.
Be suspicious if she alters her appearance and purchases. A cheating woman will try to make herself more attractive, after years of making little or no effort. She might change her hair color or style, get manicures, or start buying different, more feminine styles of clothing. New, flirty lingerie is a red flag if you notice it in her drawers, and she has not shown it to or worn it for you.
Take note if she starts spending more time "shopping." A cheating woman will claim to be out doing things that she knows her husband doesn't enjoy. Using shopping as an excuse is very common. Pay close attention to how long she was gone, and how many bags she brings home. If she was gone several hours, and comes home with one small bag from one store, chances are she was somewhere else.
Check and see if she spends more time online. A cheating spouse will use the internet to communicate with a lover.
Start worrying if she starts becoming protective of her cell phone. A cheating woman will carry her cell phone with her everywhere. If she sleeps with it and carries it to the bathroom with her now, and she didn't before, she's probably hiding something.