I came across this quote from the movie RocknRolla:

Oh, beauty is a beguiling call to death and I'm addicted to the sweet pitch of its siren. That that starts sweet ends bitter, and that which starts bitter ends sweet.

I understand the metaphor. But I'm confused with the sentence structure of

That that starts sweet ends bitter, and that which starts bitter ends sweet.

Are the first that and the that before 'which starts bitter ends sweet' conjunctions while the second that and which relative pronouns?