found his porn..

so my SO and I both have tumblr blogs and if any of you know what tumblr is or have a tumblr you know that there is easy access to a lot of porn on there. well tumblr recently got a new update where you can see what each blogger had favorites in the past and out of curiosity I went to SOs page and looked through his favorites and there was a ton of porn videos and at first it didn't bother me but I continued to scroll and as I saw more and more I started to get a sinking feeling in my stomach it was almost making me sick. 
I understand that men have their needs but my SO and I have never discussed anything like that. So I guess it was just new to me, picturing him like that? But in all honesty I was secretly hoping that after we got together he wouldn't feel the need to have to masturbate except for when I'm not around or maybe when I'm on period. 
I don't want to sound irrational but I thought that I was enough and some how seeing that makes me feel like I'm not enough. 
It doesn't bother me so much that he is masturbating as much as it bothers me that he's looking at other women while he does it. It makes me feel insecure. I want to know if I'm the only one that feels like this? or if I'm overreacting? and if you think I am then what should I do? should I tell him that I saw it and tell him how I feel? or should I just suck it up and let him keep doing what he's doing?