Based on the lines 5 and 6, what is the best meaning of treasure divine?

The answer would be a. precious item.

From the poem “ A Valentine” by Edgar Allan Poe, the poem talks about a very special woman in his life.  He had likened her as a precious item because she hold a big importance in his life. He sees her as his talisman or an amulet.

some sort of sound device i believe.

in june, we will have been married for eighteen months. (i am assuming this is what you want? the sentence, as you have presented it, is grammatically incorrect--   you want it corrected, yes? )