Farryn, despite what some people will tell you, it is not your fault you are upset about this. I understand your situation from the opposite perspective - the man's. I was in this very situation years ago and I can tell you that
- Not all men look at porn or even masturbate
- It is not "natural" to look at porn
- You should not feel guilty for being upset
In addition to feeling bad about yourself and your body (which as other people have said, is not really why he looks at porn) you might be feeling an enormous lack of trust in your boyfriend. He has been deliberately, I'm sure, keeping this from you. He is probably feeling a mixture of shame, anger, and lack of control over his addiction. The most helpful response to him may not be anger, this might just encourage it and separate you two further.
Maybe he wont have the willpower to stop looking at porn, and maybe you wont be able to stay in the relationship if he doesn't. If you do want to stay together know that it might take a lot of work and arguments to get him to stop. He might even want to stop but at this particular point not have the willpower. I can at least tell you from one man's perspective, that it is possible to work through this problem and solve it.