Boyfriend question

So I just saw a picture of this girl whom I do not know sitting on my boyfriends lab. It is a group picture with like 6 other people, and I don’t know how to react. I just texted him saying “please don’t let other girls sit on your lab” and he was like “what” so like on a scale from 1-10 how mad should I be? I’m not really the jealousy type but daaaamn....

Update: apparently she’s a lesbian🙄