WIBTAH if I told my best friend about her boyfriend's secret TikTok account?

I (24F) have a best friend (24F) who has a boyfriend (26M). I use tiktok pretty often and I was scrolling through the people recommended for me to follow. I saw this account that was recommended to me because the phone number connected to it was saved in my contacts with the name of said boyfriend. Let's say the account name is aa1234 and it said you might now "Adam Smith". So this account was connected to the phone number of my best friend's boyfriend. I had no idea he had TikTok, so I was curious to check if he had posted anything. What I saw shocked me. He was following around 300 girls, most of them half naked, and some of them ages 17-18. It was basically a collection of TikTok models, girls in bikinis, looking nothing like my friend. Also checked the date of his last repost, and it was pretty recent.

Now, if this was me and my boyfriend, I would want someone to tell me. I would find it a disrespectful and also down right creepy thing. You follow all these half-naked girls and some of them are underage??? but I don't know if I'm exaggerating this. I also don't think he would hide under a fake name on TikTok if he thought what he was doing was okay. The problem is also that me and this guy have had our friction, something about him always bothered me. I am scared he will be upset and it will come back to me, but I just feel so protective of my best friend and I think she deserves to know. So my question is: WIBTAH if I told my best friend?