Boyfriend looking at insta models

We’ve been dato for nine years and the past 6 months have been hell. constant arguing on both ends and repeatedly broken promises on his. A few months ago i saw he was in a girl we new from high school’s private nudes/sexy snapchat story. I checked who he was following after that and found a bunch of insta hoes. I explained in grave detail to him how this made me feel and why i feel it is lustful and unfaithful. skip ahead I have a weird feeling last night so asked him if he’s following inappropriate accounts and he gets SO defensive and starts questioning me. i turn it back around eventually to the original topic and he shows me his phone and of course about a dozen girls. These girls are 5-8 sizes smaller than me and look nothing like me which makes me feel like shit. Once i’ve seen it he tells me he looks at their instagrams for workouts, and that is the story he stuck with. funny thing is when i look at their pages they have close to no workouts posted. PLUS my bf is a literal gym guru and a dude so female exercises don’t make sense to me?? May I add my bf has made it a point to me literally since i met him that he finds social media models despicable. I feel like i don’t even know him, I am so upset but not even sure if it’s appropriate for me to feel this way. It seems so unnatural to me for people to look at a near naked person when ever they want. But apparently every single guy does this that i can read an on the internet so i wonder if i break up w him will the same thing happen? quite honestly i don’t think i’m satisfied with the thought that every guy does this.