15 Answers

It's usually a gut feeling. And sweetie your gut is usually right. Been there, hope it's just a stomach ache.

Sit down with him, in a quiet room, look him in the eye and ask him.  You'll know the answer.

Ducky

Might not work.

If he invites you to go on the Jerry Springer Show!!!

Ducky

Well honey, you know I love you with all my heart BUT....

If you suspect it, he probably is. 

Colleen

We don't know them from a hole in the wall. I was not about to put a lot of thought into this. The other common thought is a person who accuses another of cheating has cheated themselves in the past.

Ducky

In any case, it's ALL bad. :(

When he can't look you in the eye and say.. i love you..

If he is vague about his doings...or he cops out  the last minute prior to a planned event...if he is not where he says he's going to be...if he can't look you in the eye without flinching...if his usual scent is "off"...if the money doesn't add up...if he reassures you by telling you you're "imagining things"...if his phonecalls have become a little too private...if his paystubs are missing hours for no apparent reason...if he freaks out because you have his phone,laptop,etc....if you've got this nagging suspicion that something's just not right.....need I go on???

He comes home bathed and smells good and he says he has been to a gym but isn't losing weight. Suggest you put an extra pair of underwear in his pants the next time to let him know that you are onto him :).  And he will have a lot of "Repeated questions" to your straight question. I think that was in another question here :). If he falls asleep by 9pm, that's a definite sign and if he complains of headaches, feed him some arsenic while pretending it is Disprin ;). Several other clues, 3 mobile phones, mostly kept in his car or office but the bills come to you. They slip up usually. Just bide your time, if you want to bide your time. By the way, Liz Taylor is my idol :). 

A change in routine could be a tipoff. 
Your sex life increases or decreases.  Affection, same thing.
He is even less attentive to you when you talk than usual.
Excuses for being late or not showing up for something you have planned, missing the kids' games or performances.
Working OT without a paycheck to validate the extra time.
He needs to have more time for himself...away from home.

It's hard to have an affair with someone without making time for it.  Blocks of unexplained absences would be a tipoff. 

Have you ever followed him? Give him a cellphone with a tracker in it for a present. Then you can track him to find out where he's going.

Catch them together kissing.

Colleen

It's still cheating no matter the sexes.

Trust your gut but try to recognize that it's not plain old insecurities..............

Here's one way: http://youtu.be/7TPBh3sd29w

"When he always smiles .When going out to play !! pool with his friends.You can be sure he is "Playing but not pool.More than likely on a bar "stool with a Dolly bird.

I think it is a truely gut sick to the  stomach feeling. Sex won`t feel the same.

You can tell if a man is cheating if he leaves a 50 on the bed side table and is gone before morning.