Due to Shining Armor being preoccupied with things, he forgot his anniversary with Cadence, upsetting her greatly. He knows he needs to find a way to apologize for his actions, so Shining Armor turns to his sister Twilight and surprisingly her girlfriend Starlight.
Shining, you idiot.
Way to go Shining, now you've gotta find a way to make it up to Cadence otherwise you'll be sleeping elsewhere for months to come.
You idiot