Thunderstorm's Marble

After being visited by Cadance. Thunderstorm is shown who his true love is. But it comes at a price.

Cadance using her magic helps Thunderstorm realize who his true love is. Unfortunately while doing so Thunderstorm learns the price he has to pay. He has to get the girl to return his feelings by the end of the school year, or he will never be able to fall in love with any girl for the rest of his life.

That wouldn't be a problem if said girl wasn't Marble Pie.