This is an extremely hard one because some people can be very evasive and sneaky about it and cover their tracks well. People who have to travel in their jobs have much more freedom to cheat on their mate, but not all people do cheat even after given the opportunity.
Here are some signs of possible cheating (these are the tried and true rules):
Working a lot of over-time and you can never get them by office phone or cell.
Forgetting important dates with you or special events in your life.
Always being late for dinner and never phoning to let you know they will be late. If anything this is a lack of respect for your time.
You can never get the person no matter where you phone.
The person cheating becomes distant and their minds seem to be on other things (constantly!)
Then their is the older .. the smell of perfume on their clothing or lipstick on a piece of their clothing.
Now, before you read the above and accuse your mate of cheating, be sure you can either validate or not they are not working late. Some men especially are terrible at remembering birthdays, anniversaries, etc. If they are abscent minded they can have a lot on their mind regarding work.
The best policy is to sit and communicate with your mate. If they are cheating and refuse to admit to it then they know you are onto them, and you may get a reprieve from this, but old habits are hard to break.
As I say, catching someone cheating is very hard, so tread carefully and keep your ears and eyes open and be sure you have evidence before you accuse your mate. If not, and your mate really isn't cheating then you have broken a bond of trust with them.
He isn't cheating on her.
you will know if your cheating when you are dating someone and dating someone else at the same time.
Justin Bieber is not cheating on her.
Try, I don't know, NOT CHEATING.
The Patriots did not cheat. Therefore they could not have known they were "cheating".
If they know about each other then no, it's not technically cheating.
Ask her if shes cheating on you! Nah im kidding i dont know sorry ? :( and im a guy
Most likely in the same ways that you might know she was cheating with a man. It could even be less obvious, though, especially if she was cheating with one of her female friends.
atitude
ask him
Follow her
Ask her.