HELP! Suspicions of infidelity

How do I confront my husband with suspicions of infidelity? A few months ago he received a message from one of his girl friends late at night asking if he was home. He denied that he had been texting with her and that he had no idea why she would ask him that for no reason. The following morning I went through his contact list on his phone and saw that he had changed her name to his 7 year old niece's name. I'm assuming he did that in case she were to text him while we were together. I've checked his cellphone usage details online and it shows that they've been texting back and forth for several days. Idk how accurate this imformation is since my own usage details shows that I text 24/7 with people I don't speak to anymore. Also, that same morning that I went through his contact list, I blocked her number on his phone but it was only to see if he would unblock it back which would confirm that he has been communicating with her. I checked his phone a few days ago and the number was unblocked. What do you guys think? How do I confront him?