AIO - my boyfriend has been chatting like this with a woman in his work building

They don't work together, he just bumps into her in the common kitchen area. He's been chatting to her for at least a month, and the messages previous are deleted, they start with her saying 'I won't forgive you for airing me for a week'

To me their tone is way too flirty. I asked her and apparently he hasn't mentioned me once, until I asked him to stop talking to her. She said he also offered to buy her coffee but she refused. He also sent her images of our pottery course which he did with me, pretending it's his thing.

The woman is black texts, my bf is blue texts. She is also very typically pretty, tall and blonde with young face and blue eyes. The last image is his response to me saying I feel like he has cheated.