I desired my dust to be mingled with yours (12)
There are two ways to look at this line. The most positive way is to understand that the wife wants to be as united with her husband absolutely—she wants to be united at the molecular level. The more complex way is to see how the wife and husband give up their separate identities to the other person when they're married.
They hurt me.I grow older. (25-26)
This is a soul-crushing reaction to seeing two butterflies together. Notice how the heartbreaking image makes the wife feel that either time is slipping away, or that she's being worn down by her desire.