Thanks..that helps a lot.
My instinct on this situations tells me that unless he has given you real cause for worry (not keeping his word, not being where he says he is, not being dependable) I think you should believe him.
If he had arranged for her to be there, it would be a different story. If he has been a "stand up" guy in general, don't look for trouble where there doesn't seem to be any.
He has chosen you, you've been together for over a year. Everyone loses their virginity to someone...it doesn't mean a lifelong love. Remember that sex to a male is less emotional than it is to a woman, including the first time.
You will do far better to act confident that of course he wants you over her. Acting insecure and threatened by an insignificant contact will do nothing to strengthen your relationship. Act as if you value yourself, and it teaches other people to treat you the same way. Don't focus on the tiny negatives, like calling you the wrong name after only a month of dating when he'd been drinking. Judge him by his day to day treatment of you and his character.
Hold yourself proud and don't relive every mistake he's made. If the vast majority of the time he is dependable, trust him. Men will do almost anything to avoid feeling ashamed or inadequate...including getting defensive and backing away emotionally. You can ensure a longer relationship by recognizing and praising his good points than by focusing on his mistakes.
While no one wants to be made a fool or get hurt, I don't see anything in what you have related that sends up red flags...assuming that he is normally trustworthy.