Love is weird.
Usually it hurts, but in this case, it pretty much stabs you thirty-seven times with a kitchen knife on your birthday and then makes you go swimming in the ocean where it's salty also you can't breathe. Yeah, it's that bad.
This probably isn't a very accurate summary of the story, but I didn't really know what else to write.
…
Okay, let's get serious.

Shining Armor and Cadence were the perfect couple. Who could argue? Of course, when Shining had what may be considered an affair with a pony that later tried to take over Equestria was a rough patch in their relationship, but if it's mean to be, it'll be.
But is it? Is it meant to be?
One pony sure doesn't think so, and she is prepared to go to some extreme measures in order to separate the newly married couple, one of which includes bringing up pasts that nopony cares to remember.
It was a lie that started this, and a lie is how it will end.