I feel even more insecure than I did before

I’m a 16 year old and i have a boyfriend, we make a year on the 11th this month and the relationship is really toxic. Im not gonna go into detail about that rn tho. Basically I was on his phone just scrolling through TikTok, I didn’t go through any messages or anything extreme I was just there for TikTok. His sister is right next to me scrolling through his fyp and we went on his followings. Throughout the whole relationship he says he doesn’t text other girls nor look at other girls because “it’s too much work” and he says my body is perfect the way it is, he said I shouldn’t workout when I told him I wanted to because he doesn’t want no guys looking at me and how he’s just trying to protect me. When I saw his following feed I didn’t think much of it, it’s just video games like rust mw2 etc. but then I saw half naked girls on his following. Skinny, natural or makeup, just really attractive girls on it. I felt so insecure after that cause there was more than 5 on it. I didn’t know what to do and his sister was just there asking why there’s people showing off their ass on the app. It had me wondering if he’s talking to other girls too or is it just that because in the past 3 people told
Me he’s flirting with other girls but I didn’t believe it. I never went through anything because I do trust him but now I’m having second thoughts and I feel really insecure on how I look.