If you think that she might be unfaithful, then you should definitely be careful and look for these signs of infidelity. Just remember, do not rush to conclusions. The chances are that you are only being paranoid.

1. She is not talking to you about her life. For example, you ask her about her day and she just says: fine. Or, you ask her what is happening in her life and she says: not much. That is probably stupid. And a sign that she is sharing her life with someone else.
2. You are not the first person to know about the news. Perhaps she tells you about something exciting, however, you later learn that she already said that to someone else.
3. She changed her looks. Significantly. And she just looks different. A lot happier. She used to always be angry and now she cannot help but smile.
4. Your sex life changed. Maybe she learnt something new, maybe she is not even trying.
5. If you start talking about the changes, she gets angry and agressive. For absolutly no reason, even though you are calm.

Still, the thing may be that she just has too much going on at work and perhaps she does not want you to worry. That is why you need to have an honest and open conversation.