My Roommate Drinks Excessive Amounts Of Milk, Daily. Is This Healthy?

He should drink skimmed or 1/2 % or 2% I(t sure would cut down on the fat intake. I doubt that it is just the milk that is causing the weight problem. Remember "everything in moderation"

Your room mate, like everyone else needs to consider his overall diet rathe than focus on one thing that is "good". For thousands of years 9at least since Hyppocrates it has been recognised that  healthy life is generally a varied one, the same goes for diet. There are not really good and bad foods justt those that should be taken in larger amounts like carbohydrates and protein, and those that you only need a little of like salt and fat.
This large amount of milk will make him fat, not just on the outside, where it is an aesthetic problem, but inside around his heart where it will lead him to ill health  and an early death. He will probably already be feeling some effects, more energy needed to do less work for example. Sorry to sound so dramatic but this is the bottom line, obesity kills. A sensible limit would be one pint as part of a varied low calorie diet.
He should aim for about 2,500 calories a day, if this milk is full fat he will be getting more than this total in milk alone plus a massive and dagerous amouint of fat. (up to 350g or about 1 pound of pure animal fat). If it is semi skmmed he will still be getting over 1/2 of what his body can use in milk.
If he wants to be healthier then he would also need some exercise, but nothing too strenuous without talking to a doctor for advice on starting slow for safety. Hope this helps.