Why is my boyfriend following slutty girls on instagram?

My boyfriend and I have been living together almost 6 months now and he claims he does want to get married in the future. He also has a lot of female friends / aquantences which is not an issue for me. What I dont understand is why if some of his female friends are always posting nude/provacative photos on instagram why he feels the need or desire to follow them? Facebook is a different thing because thats not what its about but instagrams whole point is to see others photos. Why if he is serious about us and knows that it bothers me for him to see his female friends in that way does he continue to do it? Does it mean he is interested in them? Should it raise concern? I dont usually care if he hangs out with his female friends when im not around but the ones that I know are posting these pics always makes me uncomfortable when they do because I know he has seen them in this way. Is that normal?
Why is my boyfriend following slutty girls on instagram?
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