How do you tell somepony that you love them?
Rainbow Dash has no clue.
That's why she goes to see Applejack, who gives her some good old sound Apple family advice.
That's why she tells Fluttershy anyway.
That's why she tries to take Fluttershy on the perfect date, with some help and advice from her best friends.
That's why she realizes that you don't always have to tell your partner 'I love you' - you just need to show it, by doing your best to make them happy.
And if any of that happens to involve a long-awaited kiss, then that's a definite bonus.

(Link to cover artist's page: https://derpibooru.org/tags/artist-colon-nightmaremoons)