My boyfriend [18M] only likes the pictures of a certain K-pop idol on Instagram. Do you have any suggestions on what I [18F] should say or do about it?

I apologize if this explanation isn’t the clearest; it’s my first time posting. For some context, my boyfriend and I have been together since our freshman year of high school. From the start, he was always following partially nude models and frequently liking and saving their pictures. I didn’t discover this until about a year into our relationship. Although I never caught him in the act, I stumbled upon these posts when I would check his Instagram on his phone, which he was always very protective of. I’ve expressed how uncomfortable this behavior makes me, and while we’ve had a couple of discussions about it, he did unfollow those accounts and stopped liking the posts after I issued an ultimatum: if he continued, our relationship would end. Despite this, I still struggle with insecurities about both myself and our relationship, often questioning whether he truly likes me. We’ve since established some boundaries regarding this issue and haven't discussed it lately. Fast forward to now: I have access to his Instagram account and noticed that he has favorited numerous posts from a specific k-pop idol, which I’ll keep unnamed. This seems to have started about three months ago, and I’m really upset by it. The saved posts are just edits and reels featuring her, but he hasn’t liked any of them, which feels a bit strange to me. While this idol isn’t half-naked in any of the posts, it still makes me uneasy seeing only her content saved. He does like posts about other topics, but there’s nothing similar concerning her, and I’m confused about how to feel. I worry that this crosses the boundaries we set, but on the other hand, since she’s not explicit, maybe it’s not so bad? Today, I discovered links to some NSFW websites that include the idol's name while browsing his Chrome, and it made me feel sick. I haven't brought this up to him yet because I’m just exhausted from always having these conversations. I wish he understood better that these actions can be hurtful. Despite my feelings of frustration, I care deeply for him and want to make this relationship work, but I’m worn out from this behavior.