Guys would you get angry if your GF confronted you about something if you were innocent?

Theres this girl on my BF's Facebook profile and she flirts openly with him on it. He has written "In a relationship with (me)" and all there but still this girl acts like I dont even exist. I dint pay much attention to her first 3-4 flirty comments. But last time she wrote "hey how are you..bunked church this weekend? dint get to see you today". So I asked my BF whos she. He told me that shes his colleague and friend and asked "why?". I said "she looks pretty close to you". At this he got a lil angry and dint give anymore explanation and I aslo dint probe him further. Now does that mean that since they work together she has to see him everyday? She wont even leave him alone on weekends even? She dint see him for a day and she worries as to how is he? Wow!! even I dont worry that much. We are in a long distance relationship, so I dont know whats going on outside Facebook. All I get to see is in there. Please help me figure out whats going on?