I've adding some adjustments to a story of mine and I'm stuck with how to make a genuine romance between Applejack and my human protagonist.

This human has been troubled before he came to Equestria. He felt that his friends no longer cared for him. Including girls he had his eye on. When he met Applejack, he and her talk for a while during apple bucking. AJ is curious about his lack of friends and the human elaborates. He feels that his friends were just rich pricks, and he wanted to be a farm hand/cowboy. I wanted to make them feel in common that the rich always bring down the country types.

Later on, the human begins to have feelings towards AJ. Which she feels the same, but they can't admit this infatuation. So when they meet at a party, they are alone together observing the night sky.

What should I write from here resulting in them kissing?

Have them connect over something more than just class warfare.

You could have something to effect of the human expressing his dissatisfaction with his previous modern life, feeling like he has no place in a technocracy (I'm assuming he comes from the global north), and how he yearns for a simpler, agrarian existence.

or, get on the discussion of their love lives, have one of them say something to the effect of "I don't have much luck, not many folks like me like that." then the reply "I like you that way."

third option: accidental kiss. somebody trips, and the other person rolls with it.