Just discovered my fiance masturbates to pictures of girls he knows on Facebook?

My finace and I have been together for a year and a half (recently engaged) and for the last few weeks I have noticed that he has ejaculated into a tissue and thrown it in the kitchen trash before work (early morning before I am up). I don't know how long its been going on - I became privy to the situtation about 2 weeks ago. Curiosity got the best of me and I checked the history on his computer and realized that nearly every morning, he browses through the facebook profiles of roughly 15 girls that he knows. I need to preface this with saying that I do not mind or care about him viewing porn but that is not what this is. He is getting off looking at pictures of girls he knows EVERY MORNING. I am not sure what to do but he needs to be made aware that I am not comfortable with this. I know that he would not be OK if the roles were reversed and I was getting off to pictures of guys I know on Facebook. We have sex nearly every day and when we don't it is because he doesn't want to - so the reason for this is not lack of sex. Why can't he just look at porn like everyone else?!