In response to your question: You go through his wallet; you check the telephone bill for numbers called; you go through his car glove box and also his car, checking under the seats, in the trunk etc.
You check the pockets of his pants, shirts and coats. In other words, you play detective. You also need to be sensitive to changes in him. For example, does he no longer want to have sex with you? Is he buying sexier underwear? Does he have more overtime at work then he did before?
Good luck.