Am I overreacting?

My boyfriend has a tumblr which I was ok with until I saw what he was always looking at. Im very very insecure about myself and what he was looking at we a bunch of naked women. Like.. full on naked women legs spread wide open, ass in the air, an breasts just out there... it made me feel like I wasn't good enough. And to make it worse was we would be cuddling and he'd start looking at all that. An I got really mad at him cuz he knows my insecurities and he will show me some of the things and says "look at how pretty that is" and its a completely naked woman with her legs spread and bearing all..

I don't know if im overreacting or not.. but I am really really upset about this