I think all guys look at it and the guys that say they don't...well, I would hate to accuse them of lying...but...
I found a secret stash of porn once. Not that he was trying to keep it secret, I was just in a depression and he wasn't sure how I would handle it. I found it..got off myself..and then got mad just to piss him off.
But I really don't have a problem with it. I was raised around it and see nothing wrong with it.
I don't think that guys do it to compare their SO to. I think it's just sex and people, well most people, like sex. I don't watch porn much. I read erotica. I like to use my imagination more than watch it being played out for me. I like to put in my own characters, etc.
Anyway...you need to get rid of your insecurities. It's not a measure of how good or bad you are. You could have sex everyday and porn would probably still be around. Just bring it up in a non-accusatory way. Mention in general terms and ask why he watches it. Or not, I don't really think it's a big deal honestly.