AIO about finding out that my boyfriend posted his dick on r/ratemycock??

I'm gonna be completely honest: I secretly keep up with my boyfriend's reddit account. He doesn't know I know his username, but it's the same one he uses on multiple platforms so it was pretty easy to find him. And I know that's shitty but I've been keeping up on him for too long now to admit it. I wasn't entirely happy with some of the things he'd post but most of the time it was pretty standard stuff.

But I've just checked in for the first time in a couple of weeks and I've found that he's literally posted his dick on r/ratemycock a couple of days ago!! It doesn't have his face in it but it's his literal erect penis. My heart literally started pounding like a drum and I burst into tears because this feels so so out of character for him. I'm genuinely shaking. I had to just see my housemates and I wasn't able to talk or function around them because I'm so overcome by shock. Maybe it seems like I'm overreacting and this isn't a big deal but I feel like I'm having a panic attack. My chest is tight and I'm shaking.

I feel like an idiot for overreacting but I just can't believe that after 2 years of us dating he's decided that he doesn't get enough validation from me and he needs to turn to strangers on the internet for approval. And he's been texting me like normal, like nothing has happened. I feel absolutely sick to my stomach. I just love him so much and I feel like this is cheating in a minor way? Please please please I beg you to weigh in. Am I overreacting and really this isn't that big a deal??