how do you know when your bf or gf is cheating?

[jon_jon]

The only way to know if your gf or bf is cheating is to have s3x with him/her!

You can tell if she's doing some new moves and yells out some other guy's name!.. ERRRRrrr....

Yeppers she's cheating alrite.  

[Vangpao]

what are signs and clues to look out for?

You know if they're cheating if they come home with screetal on their face.

[aHMONGrican guy]

Or when she comes home and looks and smells like she just had sex and you have not duck her during the whole day yet..

[C@$H]

5 ways you can tell:

1) by way of sight: take notice of her dressing out of the ordinary, seeing her facial expressions when talking to you (guilty look, unable to make eye contacts)...most evident is seeing her with someone else.
2) by way of smell: scent of a different COLOGNE, "something  smells fishy"
3) by way of touch: she's unbearable to your touch (hands are swept away as you reach out to hold her, avoids kissing you and lack of sex).
4) by way of hearing: hearing of rumors, maybe her private conversations, but mostly when she's improperly addressing you (calling you names, talking shiet to you and/or simply the lack of communication, there of..not talking to you at all).
5) by way of taste:  her preparation of food is bland, you get left overs when she's packing lunch..worst of all you don't get to taste those sweet lips as often as you like.

[freeone]

Google is your friend. The results are pretty much true. 

[BuckFuddies2]

what are signs and clues to look out for?

When she smells like another man's cocck.

When he smells like another woman's poocee.

[AOZ]

it's a given.  if you and her are still single... cheating is expected!   

[SpottedCow]

When she starts bringin' up old dirt and the fights keep getting worse... lol.