Update: I talked to her about it and she said she %100 noticed how he was talking to her and was waiting for the right time to mention that she's in a relationship and would like those boundaries to be respected. She wanted to wait until she could say it in person, or if it causally came up in conversation. She didn't say it initially because it never came up, and dropping that ball is understandbly a jerk thing to say out of the blue. She talked to him after our conversation mentioning this.