Boyfriend lied about woman at work

For context, he deleted a conversation with a female colleague containing a voice memo. This worried me, so I confronted him - turns out, the messages contained a voice memo of a conversation that he had with ANOTHER female colleague. During the voice memo, the female colleague was essentially expressing her hurt for the way he had been treating her. She claimed that he was being distant, cold, and a “shitty friend.” My boyfriend responded with corporate jargon, basically saying that he did not want to cross any professional boundaries, and that he was trying to navigate his “new relationship.” This part is what made alarm bells go off in my head. The girl proceeded to laugh, stating that she was cool with our relationship, and emphasizing the fact that she had brought me a shot before. I knew was boyfriend was semi-talking to another girl shortly before we got together, but he never disclosed that it was his coworker. I didn’t even know I had met her! I asked why he recorded the conversation, and he stated that it was for his own protection, because “she has a history of getting men in trouble with HR.” He claims that he didn’t want her to accuse him of doing something inappropriate, and falsely accuse him of something he didn’t do. I feel like he’s lying. When he speaks of her, he does not have a single good thing to say. My boyfriend says that everyone picks up her slack, that she posses red flags similar to his ex, and that she makes everything about herself. He tried to emphasize the fact that he would never cheat on me, but that wasn’t the point. The point was that he lied, and purposefully hid her identity from me. He is perfect in every other way, and I know he truly loves me; but I am so hurt. He is my best friend, but I feel like I’ve lost trust, even though it seems so small. AITAH?