My boyfriend is very private and I caught him in lies..but he promises he's not a cheater?

Look, if he's lying about something so small as what his middle name is, he can lie about anything. I wouldn't trust him. He needs to start being honest or else you need to get out of that relationship. It honestly seems kind of dangerous. You're going to get your heart broken. You already found evidence that another girl was there, just be careful. He says these things, and they are lies. Why should you not think that other things he says like he "has never cheated" is true? Be cautious!