You and your last BF were cuter than Justin and Selena. Things were so, so amazing... until you messed up in a major way. Now it's over and it's All. Your. Fault. No matter what you did to cause the rift in your relationship, follow our advice to shake that guy guilt and become a better GF in the futurejust in time for the first day of school. P.S. If you've never had a BF or are flying solo right now, this is your cue to take notes. You can avoid these relationship ruiners when you are single no more.

YOU CHEATED

GUILTY GAL: Relationships shouldn't be mathematically complicated: One plus one equals couple. The definition of cheating may be different for everyone, but you know that bringing another "one" into your life totally crossed the line. . .and unfortunately, so does your ex.

WHAT NOW: Think back to your dating days with your former BE Why exactly did you cheat? Were you unhappy with him? Did you get bored? Was it hard to control your wandering eye? Whatever it was, you don't want to be known as "the girl who cheats" (talk about ruining your chances with a future flame!). So next time you're tempted by someone else, think about what you have in front of you. If you don't want him, break it off right away - don't go behind his back.

YOU WERE DEMANDING

GUILTY GAU You freaked if he didn't text back ASAP. You fumed when he hung out with his crew instead of you. You held a grudge for days that time he didn't wave at you in the stands during his soccer match. You held him to crazy standards... and he finally decided to walk away for good.

WHAT NOW: This is real life, not a romcom. Your BF was not put on earth to fulfill your every relationship wish. Before diving headfirst into another romance, adjust your expectations. Sure, someone you're dating should pay attention to you. But instead of expecting him to jump at your every command, give him space and let him have his own life the way you have yours. That's what makes you both even more interesting.

YOU GOT (REALLY, REALLY) JEALOUS

GUILTY GAL: A little jealousy is normal when you think about your BF hanging out with other girls. But you unleashed that envy and couldn't reel it in. . .and it got the best of your relationship.

WHAT NOW: Give yourself an ego boost. Chances are, you got green 'cause you were a wee bit insecure about where you stood with your guy. Going forward, remember to remind yourself about all the things that make you oh-so fab. And communicate, why don't ya? A trusting, open relationship will banish the green monster for good. By staying confident in yourself - and your relationship - you can bid a not-so-fond farewell to your jealous feelings.

YOU CHICKENED OUT

GUILTY GAL: You were desperate for a BE. .until you got one. Then, the idea of opening up to a guy? Going on dates? Kissing? Eek. You fled faster than Usain Bolt at the Olympics.

WHAT NOW: Take a deep breath and remember you are never obligated to do something that doesn't feel right to you. If you're not ready, you're not ready. But another thing to remember? Sometimes you do have to push yourself outside your comfort zone and take risks in order to get what you really want in the end. Plus, talking to (and dating) guys will get easier in time, we promise.

YOU FELL OUT OF LOVE

GUILTY GAL: Your ex was head over heels while unfortunately your feelings were fizzling fast. You let him go, and now you're wondering if you should have stuck it out.

WHAT NOW: Know that you can't force yourself to love someone, and besides, relationships only work when both of you are equally into each other. Truth is, it's better to get out of the relationship than pretend you like him as much as he likes you - or worse, to wait for those feelings to "come back" again. That's only leading him on. Chin up! You will find someone who makes ya feel those fireworks again.