A teenager hunts the killer of his father but falls in love with the daughter of his enemy. Can he kill the beloved father of the woman he loves?

I see this as a Southern Crime/Romance story.
In the likes of "Mud" and "Monster's Ball"

That sounds just like Romeo and Juliet. The setting, the part of society they are in will make or break the film. I'd suggest creating a 'world they live in' and use that as why he finds himself in that situation.

You can focus on many different directions with this plot. You can focus on the main character trying to kill her father without her knowing, or the character attempting to find another way of justice, or have the character debating over his choices, or have him choose love over vengance. The debate is endless. Good work, you have freedom to branch out.