They Never Tell You Their Whereabouts
This is a major one. It is not necessary to know your partner’s whereabouts at all times but if they don’t tell you when you ask them it might mean that they are hiding something from you.
On the surface, it might not seem like a big deal but if they are withholding something from you it means that they don’t want you to know something about their private life. These things go hand in hand. There is a secret they are not telling you about.
If they are not telling you where they have been they also don’t want you to know with whom they were with. In these situations, it is very natural to guess that they are cheating on you.
Remember that they wouldn’t act like that if they didn’t have something to hide unless of course, they spend time playing World of Warcraft in a friend’s basement – who knows that might be possible, though the chance that your partner is playing WoW instead of cheating is slim.