Believe what you see. If your partner is doing the work of recovery and you see continued evidence of this, perhaps there is reason to begin to have trust again. While it is not healthy for you to be in the role of checking up on your partner like a detective, you will soon see evidence that he or she is or is not worthy of trust.
Believe your feelings. Learn once again to listen to your inner voice. Unfortunately, many partners have learned not to trust their feelings because the sex addict was so convincing in the past. He or she may have gone to extraordinary lengths to persuade you not to trust your feelings. In the past you denied suspicions and dismissed the inner voice telling you that something was going on behind your back. You convinced yourself it was all in your mind, or your partner convinced you to trust his or her version of the truth and not your own reality.
Part of taking care of yourself is realizing that you can trust your feelings and your inner voice.
direct excerpt from "Stop Sex Addiction - Real Hope, True Freedom For Sex Addicts and Partners" by Milton S. Magness.