Could she be cheating?

About 9 years ago my wife cheated on me. We worked through it and moved on. Well, a few months ago I noticed a new number on her phone records that she's been texting a lot and calling a little bit. I've looked in her phone but those text conversations have been deleted. I've called that number from different phones but they never answer, it always goes to voicemail. I've done a reverse look-up but the number comes back unlisted. She has the number stored in her phone under her cousins name, but I've been with her for 17 years and she hardly ever speaks to her. And plus, if that's her cousin why would she always delete their text conversations? Worrying about this has really taken a toll on me, because if its true, then it will definitely destroy our marriage and our family. What do you all think and how should I approach it? Any suggestions on what I should do would be appreciated. Thank you!