Remember that you can love them both without them necessarily having to enjoy each other.
This goes for friends and partners who haven't dated, too, now that I think of it. Don't ask your man if you're prettier/smarter/better at Scrabble than his last girlfriend.
Save it for your diary or for anyone who didn't date him. This can be extremely tempting if they ended on bad terms and you know you'll find a sympathetic ear.
However, in order to maintain a healthy relationship with both of them, it's crucial that you never seem even a little like you're taking sides in their breakup or casting either one as the bad guy, even months or years after the fact. For instance, if your friend doesn't want to go to parties where her ex will be in attendance, don't pressure her.
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