Dear Em & Lo,

I am so confused and upset. I recently found that my ex-boyfriend and a girl who I thought was a close friend of mine have been dating behind my back.

The back story is that he and I dated for a year and broke up a year and a half ago when he got back together with his ex-girlfriend (who had been engaged). My friend, S, had been dating his best friend for about a year, and she broke up with him for her ex as well. S and I remained friends throughout this. She knew how hard my break-up was. Anyway, it’s a year and a half later and they are both single and now are sleeping together and “dating casually.”

I know their actions together have nothing to do with me. I just wonder — I thought it was uncool to hook up or date your friend’s ex. Am I overreacting? My heart feels broken over what someone I thought was a friend did.

— Brokenhearted in Brooklyn

Dear BiB,

Um, wait, we missed the part where their actions have nothing to do with you. Not true! She’s your close friend and he’s your long-time serious ex. Whether they admit it or not, when they bump uglies it has everything to do with you… at least, so long as it’s breaking your heart, it does. Especially if they’re doing it behind your back. So low!

As a general rule, we think it’s bad manners — not to mention bad taste — to date or sleep with a friend’s ex, a.k.a. “dating the floor model.” Why ruin a perfectly good friendship for a hook-up that, let’s face it, probably won’t last the season? The ONLY way we think it’s acceptable to move in on a friend’s ex is to (a) wait until that friend has reached some kind of relationship closure (that clearly hasn’t happened here), (b) give the friend a heads up first so they’re not blindsided by the news (er, again, your friend seriously failed you here), and (c) only do this if you’re convinced that there’s some kind of deep love connection and that you’d be defying Cupid to ignore it (once again, totally not the case here). In other words, yep, what your friend did was 100% uncool. No wonder you’re brokenhearted!

We also think it’s uncool of your ex to do this too, but whatever — you expect exes to act like assholes. That’s why they’re exes, after all.

But back to your “friend.” Not only is she kinda screwing you over, she’s kinda screwing her ex over by dating his BFF too! Talk about a double whammy. If you really value whatserfuck’s friendship and think she deserves a second chance, then confront her on the matter, explain how hurt you are, and see what kind of defense she has to offer. You don’t have to accept her defense, of course — we’re having trouble imagining a good excuse for this situation: “Ohhhhhh riiiiiight…THAT was the guy who put your heart through the blender! I didn’t recognize him without the goatee!”

We guess it could just be a matter of the forbidden being all the more tempting, of obstacles (or in this case morals) standing in the way of love (or lust) thereby making it all the more appealing. That’s the nature of the beast. But there’s Romeo and Juliet, and then there’s Gossip Girl.

If she gives you one of these excuses and you buy it — great! You’ll have gotten the closure you deserve. If, on the other hand, she gives you one of these excuses and you don’t buy it — or if you can’t be bothered with a big Talk and just want to cut to the chase — then go ahead and bench her. Because dating is hard enough on the heart when your friends have your back. But when they don’t? It’s soul-destroying.

Your friends,

Em & Lo

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