Think about it this way, what difference would it make if those women were'nt professionals or you knew them personally? How is it different to you havin naked pictures of the hot girl at work?
Actually I personally /don't/ have a problem with my boyfriend looking at other women (not that he would) but that's how she sees it. But if you find out your partner is really into porn she could be wondering what sick fantasies do you have, where did those girls comer from, what do you expect from her in bed, what pornstar are you comparing her too subconsciously, is she not sexy enough to be all you need etc. Again, I don't care what he does because I know he loves me and has a good heart. If she is freaking about your some porn, there is a deeper issue going on.