I have lost my mind please help!?

I have been dateing this guy for 9 months we never fight. We see each orther 3 times a week and we never argue maybe once a month usually small bickering and then we get over it. We do alot of fun things together blah blah blah you get the point were good together. The main point is this i had begun looking through his phone about 5 months ago and their was this number that kept on apperaing in his phone sexual remarks back and forth no name just a number so i wrote it down a month ago and had the nerve to call it yesterday and a guy answered the phone and said his name was sal and he was the owner of the phone that this was not a girls phone number i apologized and said i had dialed the worng number. My boyfriend told me this number belonged to a girl named sally when i asked him about the text back and forth he stated that she would call him for sex but he never called back. Dont most of us when we lie about someone change their name use the first letter and change the rest of the name? or could it be ironic that their is a girl name sally and a guy named sal in his phone with the same number? Or is my boyfriend bi sexual? And how do i confront him about this situation?