This entire thread is why, after my first year, I always ALWAYS, even if I had to cheat or scam, had a roommate I was already good friends with.
I had this problem. My response was to make popcorn while they were having sex or just in bed together and watch intently after about the sixth night.
He retaliated by downloading horse porn onto my computer (he didn’t have one so up to that point I let him use mine).
I retaliated when I had my chance–he’d got into some kinda trouble with the fraternity that he was pledging, and retaliated by stealing some paddles. Then he stole their barstools and some photo albums. I got back from class and his side of the room looked like John Belushi’s rummage sale. Found out that he was only not in the room because he and his best friend were stealing some fraternity brother’s car.
When the guys from the frat came looking for him, he still wasn’t back. I let ‘em in, pointed to the masking-tape line on the floor, and excused myself to grab a shower (I’d been putting it off after fencing, surfing the net being WAY more important.) Besides, I knew one of the guys from engineering classes (he was a TA in somethin’). When I got back, not only was EVERYTHING on his side of the room except his bedframe (no mattress) and half his desk gone, but I had absolutely plausible deniability because no one ever locked doors to go to the shower–especially us, we were right across the hall from the bathroom.
In closing, I guess I suggest Dinsdale’s kid get some random third party to temporarily destroy the roommate’s life for unclear reasons. 
After that I only had one trouble with him. He came home around 3AM stoned off his ass and started blasting either the Dead or Phish, which is fine but not at 90dB at 3AM. So I beat him into incoherency (in fairness this amounted to two gut punches and shoving him onto his bed) stole the power cord from his stereo and locked it in my desk, and gave it back in the morning. I don’t even think he remembered me forcibly putting his ass to bed.
Shit, when I had to get laid, I ASKED my roommate. We had a SYSTEM. Well, that and we all had at least one night class on a night our roommate was home, so that and lunch break quickies were designated gettin’-laid time. Hell, at one point 6’1" 230lb me and my pleasantly curvy and 6’4" girlfriend had sex in the back of her Focus hatchback barely pulled off a only somewhat busy highway, because I “needed to get laid” (it seems that way at 19) but my roommate had to study. I should get a medal for that.