Am I pissing him off?

You can not. The trouble with texting is that we remember the stuff we read for longer than we do the stuff we only hear. I understand why you felt the need to ask this guy if he was still involved with your friend, but when he said no, you should have left it there and not given him details about what she said to you and how you think she feels towards him. Tell him that you are sorry for over-reacting and, if he agrees, would like to put this episode in the past and leave it there because you do not want to damage your relationship with him over something that is really a lot less important than you felt it was at first.