My boyfriends friend posts her nudes online...

My boyfriend of 5 years, has this friend who posts her sexual pictures on Instagram/Facebook. I'm talking bra, thong, lingerie... bdsm shit (tied up, ball gagged, butt plug) -- and I've always tried to be okay with him seeing her posts all the time but its just so hard to get over when they hang out, and all I can think about it how he has seen her nudes. I keep pushing it to the back of my mind, trying not to let it bother me anymore. But today, an acquaintance actually messaged me and asked me if I knew my bf was liking this girls nudes on Instagram because they didnt think it was appropriate and wanted to let me know what was happening. I got curious, and checked out her page( its public ) and sure enough he likes all her posts. It feels wrong to me, to look at/like someone elses nudes when you're in a relationship...

I dont want to be that controlling girlfriend that makes their bf stop being friends with someone. I dont want to do that. I trust that he will never do anything with her. But it makes me feel uneasy. Am I wrong to feel this way?