Likewise, don't grill your boyfriend on what went wrong or insist that he account for his behavior throughout the entire time they dated.Their relationship is between them; it's not your cautionary tale or your soap opera. It's easier, of course, to have hard-line rules — "exes are never OK" versus "exes are totally fine" — but that's not the world we live in.If they choose to share details with you, that's fine — you don't need to stick your fingers in your ears, unless an overt comparison is being made (see No. Your relationship and theirs are separate things, and you don't need to know anything they don't care to tell you. If someone seriously mistreated your friend (we're talking emotional or physical abuse, infidelity, lying, stealing, etc.), don't date him, no matter how awesome his butt looks in jeans.This has nothing to do with some kind of Eternal Dibs situation, and everything to do with the fact that, by choosing to build a relationship with someone who treated her horribly, you're telling your friend you don't think what he did to her was all that bad. There are lots of people out there who are just as good in bed and haven't traumatized anyone you care about.Set the precedent that people who are awful to your friends are people who don't get to see you naked, and your life will be the better because of it.RELATED: 22 Reasons to Stop Worrying About His Ex-Girlfriend17 Things I Wish I'd Known About Getting Over an Ex When I Was Younger11 Reasons Why He Broke Up With You Follow Lindsay on Twitter.
What I've noticed, though, is that every person I've heard espouse this worldview was straight.
Set aside time for each of them and honor it — don't drag your lover along on girls' night out (not even if your lover is a lady; queer chicks are 4. Don't ask your man if you're prettier/smarter/better at Scrabble than his last girlfriend.
Don't do this ever, but especially not if his last girlfriend is the person you're going rock climbing with Sunday.
Trust that your dude is with you because he likes you and you're awesome, not because he's biding his time until your friend takes him back.
Trust that your friend is happy you've found someone you dig, not plotting to sabotage your love.
We know our backstories will be tangled and intertwined.