1. He’s been unfaithful in the past.
2. You’ve caught him lying, even about simple things.
3. Lack of intimacy.
4. He’s distant, physically and emotionally.
5. He avoids the topic of cheating and deflects blame onto you/changes the subject.
6. He compares you to other women/asks you to change things about yourself.
7. He ignores you/treats you poorly.
8. He chooses to spend his free time alone or “out,” rather than with you.
9. Secretive cell phone behavior, such as deleted contacts and use of passwords.
10. He’s rarely apologetic after an argument/his apologies feel insincere.
Most of all, your intuition tells you something is wrong. You don't always need concrete evidence that he's cheating on you. Even if you can't put your finger on it, don't dismiss your feelings.