The cheat sheet: "think your boyfriend might be doing you wrong? Here's the smart girl's guide to exposing his cheating heart.

You might never understand why guys cheat, but you can learn to recognize if your guy is cutting out on you. We'd never want you to turn paranoid-stalker, and don't dare invade his privacy. But if you keep your peepers open, you can pick up on those subtle clues that give away ... Da Playa.

SUSPICIOUS SITCH You're at Taco Bell with your boy when his cell rings. He shuts off the ringer and shoves a Cheesy Gordita Crunch into his face.

CUT HIM LOOSE If your guy's relationship to his cellie has gone wacky, keep your antennae up. Especially tune in if he has assigned ringtones and ignores a certain one when you're in his airspace. He abruptly ends convos, or leaves the room every time he takes or makes a call? He could be cheating. Either that or he's planning your surprise birthday bash.

CUT HIM SLACK Erratic phone behavior can be a sign your guy has someone on the side, but don't be quick to accuse. If he glances at his caller ID and says, "It's just Jeremy reminding me of practice," it could be. Most boys don't like to gab on the phone and, sometimes, nothing can come between a guy and his Gordita.

SUSPICIOUS SITCH You and your BF used to clock in all kindsa hang time. Not now. He even ditched your movie plans last Friday to go out with the guys.

CUT HIM LOOSE Take this GL mini-quiz: 1) Does he A: stand you up or B: give you notice so you can make other plans? 2) Has he A: made a habit of dissing, or B: changed up the routine but still sees you? 3) Is he A: rarely reachable, or B: staying connected? Scoring: If you answered Mostly As, there's a shot your sweetie is stepping out. Mostly B's? Read on....

CUT HIM SLACK Your guy might need some space. As long as he's keeping in contact and being respectful, let him have his breathing room. Basking in his comic book collection or shooting hoops with his pals is not cheating. So savor your individuality. It's so much more attractive than being cling-on girl.

SUSPICIOUS SITCH He tells you he's headed to Bud's house to play Gran Turismo. Thing is, he's all dressed up and smelling like Axe (ew).

CUT HIM LOOSE A dude who, outta the blue, cares about his appearance might be trying to impress someone special. If this boy never decks out for you and, in fact, rarely even remembers deodorant ... well, must we spell it out for you?

CUT HIM SLACK It is possible, however, that your guy is suddenly taking an interest in his hygiene because he's actually starting to (gasp!) mature. As long as his dressing-to-the-nines isn't selectively timed, embrace his new well-groomed ways. Tell him how hot he looks--then, give him a gift of CK Crave for the holidays and hope he nixes the Axe.

SUSPICIOUS SITCH It's the night of the big dance, and you feel like you're on a date with some Laguna Beach loser. He won't even dance with you.

CUT HIM LOOSE It's obvious this guy is eyeing Jen on the other side of the gym. And last weekend, when you guys ran into her at the football game, things were way awkward between those two. Thing is, if you sense something is up ... something is probably up.

CUT HIM SLACK Then again, maybe his only sin is that he doesn't know how to dance and is too embarrassed to admit that to you. Offer to give him a private lesson so you two can get your groove on at the next soiree. And if Jen tries to cut in? See above paragraph.