Complex sentence: While at bat, Jason has a lot more on his mind than the game; he is trying to decide which girls to invite to his bar mitzvah: the girls he should invite or the girls he "wants" to invite.
Split into simpler sentences: While at bat, Jason has a lot more on his mind than the game. He is trying to decide which girls to invite to his bar mitzvah: the girls he should invite, or the girls he "wants" to invite.