The one who seduced you and fucked you over and broke your heart in a million pieces and laughed about it: Glee. Obviously the answer is Glee. I can hear Ryan Murphy's laughter in my nightmares even now.
The old flame you don't see very often any more but whom you still really enjoy getting together with for a few drinks and maybe a pleasant nostalgic romp in the sheets: The Class. It's like my comedic touchstone. Kat Warbler, NEVER NOT THE BEST.
The mysterious dark gothy one whom you used to sit up with talking until 3 a.m. at weird coffeehouses and with whom you were quite smitten until you realized he really was fucking crazy: SLEEPY HOLLOW.
The one you spent a whole weekend in bed with and who drank up all your liquor, and whom you'd still really like to fuck again although you're relieved he doesn't actually live in town: Moonlight. We had a legendary literal-weekend romance, and I'd like to know if I could get that ship magic back, because my default reaction is always "but vampires tho."
The steady: The Office. We even have a standing date 5 nights a week. At midnight. Also, Jim/Pam is holding the official crown for #1 OTP Of All Time for as long as they possibly can -- eight years and counting.
The alluring strangers whom you've flirted with at parties but have never gotten really serious with: Leverage. You seem cool! I wanna hang! Coordinating our schedules, on the other hand, has been consistently problematic.
The one you hang out with and have vague fantasies about maybe having a thing with but ultimately you're just good buddies 'cause the friendship is there but the chemistry ain't: Cougar Town. It's nice to see a friendly face at 2 AM when nothing else is on, but then we go our separate ways until the next time I'm up too late.
The one your friends keep introducing you to and who seems like a hell of a cool guy except it's never really gone anywhere: Gilmore Girls. I worry it might be too late to love it with the eyes of an early-2000s kid.
The one who's slept with all your friends, and you keep looking at him and thinking, "him? how the hell did he land all these cool babes?": Avengers. Always Avengers/MCU/whatever that conglomerate mess of superheroes is called.
P.S. My answer to this question on the last meme was Supernatural, which is not only STILL AROUND, but given its ability to suck in Glee fans to this day, is also still an accurate answer.
The one your friend has fallen for like a ton of bricks and whom she keeps babbling to you about on the phone for hours, and you'd be happy for her except you just know it's going to end badly: I need more time to ponder this one. The last thing people liked that I expected to fail was Reign, and it's on season 3. What do people even like these days?