How can you tell when your man has cheated with someone?

well there are signs i suppose like when they arent acting the same around you and are more secretive about doing certain things around you like checking emails or texts or even answer a mobile. sometimes there even smarter and be very sly on what they do allow you to see rather then hiding everything from you so you arent as suspicious all guys are different iff you message back and tell me how he's acting with you i may be able to help see through and tell you whats happening with your relationship and him.