I need advice

So my bf has been secretly talking to this girl at work for months and I’m now just finding out about it and the past few days he’s been adding her and un adding her on snap. And saying she’s perfect And he wants to be with her. And he said he didn’t mean it. And he’s always trying to make the conversation about him. He’s acting like he don’t care about what he did. He’s been secretly talking to her for months bought her sum bec she asked him to. Looking at pictures of her. And he’s saying that all of it is my fault. He’s basically saying that it’s ok for him to have secret conversations with some girl but I can’t tell his manager what’s been going on. He always finds a way to make things about him. He gets caught and he makes people feel bad for him or he get angry.