A lonely teenager becomes romantically involved with a girl who recently lost her sister, after he fabricates the death of his twin brother, who abandoned him to attend a soccer-team summer camp.

I agree with why.kim, "who abandoned ..." just confuses the sentence, it also shortens the Logline for the better. "his twin brother's death" may read better than "the death of his twin brother" - makes it even shorter!

Hey, thanks for the reply! I completely agree. Initially I thought that including that might have counterbalanced any negativity felt towards the protag, as a result of the story being based around one of his lies, but in hindsight, all it does is jumble the logline.

Don't think you need the "who abandoned ..." part.