I assume that you have access to your phone records. For most providers, you can look up every call that has been made or received very easily. It will show you the time of the call, duration of the call, and phone number. Obviously, there is a good chance that the same number has been called many, many times over a significant period of time. More important, prepare yourself emotionally as best you can for what you are going to learn. This kind of news can be devastating. Make a plan for how you will stay sober if you learn that your spouse is cheating on you. Good luck. I'm sorry this is happening.