Bonus: the guy who plays the drug dealing patient is Ethan Embry, who was also the star of the short-lived, way ahead of its time FreakyLinks, which I, as an adolescent who loved The X Files, devoured.
Anyway, first they thought that drug dealer had some sort of inner-ear imbalance or brain tumor, but after both those hypotheses turn out to be null, they let him go with the idea that they'll follow him to his secret drug lair and test the environment for toxins. This didn't work, because he managed to lose the tail composed of Thirteen and Cameron. Luckily for the gang, he was right back in the hospital with worsening symptoms the next day.
Isn't it convenient how that always works out?
Also, there's an ongoing "practical joke" everyone on the team is playing on Foreman, pretending they get paid more than him. Apparently, this was mean to "bring him down a few notches"? Yes, doctors, pay discrepancy, especially for the only minority person on a team of equals, is HILARIOUS.
Eventually, we find out that drug dealer has been taking beta blockers to deal with all the stress of, you know, dealing drugs, which caused one of his original symptoms. With that off the table, the team is able to come with a new potential diagnosis, and start testing.
While all this is going on, Wilson and House have moved into their new apartment. While meeting the new neighbors, Wilson found someone he'd like to date. After she makes the mistake of thinking he and House are more than just roommates (hence the title), he enlists House's help to convince her that they're not gay. He decides to act really gay, in the hopes of eventually seducing her. The plan is very convoluted.
After making use of his amazing powers of deduction, House figures out that drug dealer is actually a cop, which is why he's been taking beta blockers - to hide shaky hands, sweating, trembling voice. All would be symptoms if you had to be a bad guy when you were really a good guy.
The cop gets worse and worse, and all the while, it becomes clear that the drug dealer guys are actually pretty nice, helping him out, risking their own hide by letting Thirteen go to the storage facility (a dry cleaners!) to look for environmental toxins. We find out that there's a big police bust coming that night, which is why the cop didn't want to tell anything about the operation, so it wouldn't be compromised. To make matters more confusing for Ethan Embry, his drug dealer buddy makes a heartfelt speech about what close friends they are. Oh Ethan, I bet you're feeling pretty conflicted right about now!
On the unequal pay distribution front, Foreman reveals to the team that he asked Cuddy for a raise, and after she refused, he decided to leave the hospital in search of greener pastures. The other three freak out, and rush to Cuddy to try and make amends. They offer to each take a pay cut so Cuddy can give Foreman a raise so he'll stay. After they make the agreement, it turns out that there was no other job, Foreman didn't really talk to Cuddy, and managed to manipulate them into giving him part of their paychecks. Haha - payback is delicious! I definitely did not see it coming, and this was about the only good way this storyline could have resolved itself. Well played, House.
Sadly for the cop, it turns out he has a rare and aggressive auto-immune disease that will kill him within the next 48 hours. He finally calls his wife, whom he hasn't seen in 16 months, and she's there as he draws his last breath. The bust goes as planned in the drug den, and all the bad guys, including the cop's buddy, gets taken in. Oh, and House reveals to the lady that he's not really gay, and she's mad at both of them.
The lesson in all this? Don't prank your friends about money, don't pretend to be gay to win the ladies, and don't go undercover with hardened criminals. Three solid pieces of advice, House.