Alas, the logline is:
1] Too long (41 words).
2] Too complicated to understand the plot in one quick read (which is how loglines are read).
3] A logline should only raise one question in the mind of a reader: "Will the protagonist achieve his objective goal?"
But this logline raises numerous questions, like:? What does it mean that worlds mate?? How do they mate?? ?What worlds are there beside the world we live on?? Open gates to both worlds?? What gates?? How will his death keep the gates open forever and doom mankind?
fwiw