The one who seduced you and fucked you over and broke your heart in a million pieces and laughed about it: Avatar.
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: Buffy, Saiyuki.
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: Battlestar Galactica
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: Black Lagoon. Only I wish she lived in town.
The steady: Naruto. (And the fact that this has changed since the last time I did this meme tells you how steady my steadies are).
The alluring stranger whom you've flirted with at parties but have never gotten really serious with: Bacanno!, Princess Tutu.
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: Leverage, How I Met Your Mother.
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:
Neon Genesis Evangelion.
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?": Hetelia, TTGL.
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: Hetalia, Bleach.
The ones you repeatedly cheat on your steady with: Black Lagoon, Avatar.