My boyfriend (19M) said I (19F) broke one of his boundaries makes me feel like I won’t ever be able to do anything right. How do I go about this?

I decided to share with my boyfriend about how I asked for help on another subreddit about workouts I could do to help my scoliosis. In the post I had posted a photo of my back, without a bra on. However nothing about my front was visible at all as the photo only showed my back. He asked if he could see the photo and I tried to explain how it was a big insecurity of mine (how my back looks) and I just didn’t want him to have a photo that he can stare at for however long he wants of my back. Yes he has seen my back before, I just didn’t want him having a clear photo that shows my insecurity. He got upset about this, and decided to somehow found my reddit post. When he found it he was outraged and said that I was posting “naked photos of myself” and that I had broken that boundary. He didn’t appreciate how you could see the beginning of my hips in the photo and said it was insane I would ever post something like that. He mentioned how I should have asked his permission first. I tried to explain that I didn’t do it out of ill intent or too seek attention in a weird way, but that I simply was asking for help. You can even see in the post description how I only was asking for workout tips. However he told me directly that he does not care what the reason is (this is a recurring thing) and that the only thing that matters is that I did something extremely bad (posting a “naked “ photo.) I told him that nobody even saw it as sexual (except one creep who commented about needing to see the front to determine the workout) and he proceeded to get more upset trying to use the creep as leverage that I was posting provocative photos. I simply don’t know what to do, or how to communicate to him that it is unfair to treat me as if I posted the photo with bad intentions when I did not. I just feel defeated and slut shamed for something that I don’t really believe was all that bad. I was just asking for help.