While I have no doubts that there exists evidence (from a biological and psychological point of view) which demonstrates some of the ill effects of pornography (and other illicit forms of sexual stimulation), I think this is a case where it is hard to divorce one truth from another.
For example, it is true that even an Orthodox Christian can say that the relatively new secular science of psychology (in reality, it has existed for centuries in the Church) has garnerned some interesting insights, it is ultimatly unprepared to offer any important solutions to anyone. Case in point - psychology tries to explain and perhaps cure abbherant behaviours. Yet, if you ask most psychologists, they could not tell you what normal in fact is (!!) in most cases, if any.
Now tell me - how can someone help you "become normal" if they are not even sure what "normality" is? The situation becomes even worse, when the therapist/doctor in question does believe they know what "normal" is - but this "normality" is being dictated solely by popular/cultural consensus, and is not the normality illustrated by God's Law, let alone Personified in the Person of our Lord Jesus Christ.
Thus, while I'm sure you can find evidence for the health (whether physical or psychological) side effects of indulging in pornography, oggling women, fornication, etc... this is an area of Christian moral teaching which doesn't stand on it's own. Indeed, I think it opens up a larger subject - the purpose of morality in general.
Most people (and your friend is probably included in this) now understand "morals" to exist primarily on a social contract basis - I won't steal your stuff, if you don't steal mine, etc. etc. However, this is not the moral outlook of the Church. Nominally, morality exists because it is what the Spirit has revealed to mankind - we do as God asks. However, more deeply, "morality" exists, for it's observance is a condition necessary for those who will be reconciled to God. IOW, we abstain from doing certain things, because they blind our ability to acquire the vision of God (theoria), or create affections and attachments which wage war against what should be our primary love (God.)
Without this outlook, a great deal of what the Scriptures and the Church teach to be "immoral" (such as indulging in pornography) makes little sense. Certainly from a secular "social contract" basis, it's hard to see what is "so wrong" with looking at pictures of naked women (particularly if the women in these pictures were consenting, and it cannot be demonstrated with certainty that there is an immediate link between me doing such, and then going out and raping someone.)
While of course, given that it was God made us, and God reigns throughout this universe (whether individual men choose to acknowledge this or not), it is also going to be true that ignorantly (?) ignoring His Laws is going to result in misery, such is nearly impossible to demonstrate in any meaningful way, when divorced from the "big picture" (what man's primary goal in life should be, which is union with God in Jesus Christ.)
I don't know your room-mate's background or beliefs - but I can suspect that at the very least, he does not take this Christian "big picture" very seriously. Given this, I am not even convinced what the long term value would be of even correcting his behaviour in this regard - a Godless person who, for whatever reason, chooses not to oggle naked women?
I hope you can see then, that even the virtue of chastity (or anything else for that matter), when divorced from God, is really of no meaning.
While you can make it clear to your friend that you do not approve of his behaviour in this area, and would appreciate it if he didn't subject you to it, perhaps a better thing you can do for him (besides praying for him) would be to discuss more basic (and ultimatly more important) things with him, like God, and the Gospel of Jesus Christ.