We debated over whether we should label this theme "lust" instead of "love." When Cupid's golden arrow nails Apollo, making him fall for Daphne, Apollo doesn't seem exactly in love with Daphne. Instead, this god of reason seems overwhelmed with irrational, overpowering erotic desire. Cupid (a.k.a. Eros) was the god of desire after all, not love (that was the job of his mother, Aphrodite/Venus).
However, when Daphne's father turns her into a laurel tree to protect her from the love-crazy god, Apollo seems sincerely moved by what's happened. He honors Daphne for all time by making the laurel his sacred tree, keeping her memory always close to his heart. Sure, we can debate whether being transformed into a tree is worth the "honor" of being sacred to Apollo, but it seems clear that Apollo has developed something deeper than his initial wild desire for Daphne.
Overall, though, love is tragic in this story. It's also causes total chaos. Neither Apollo nor Daphne ends up happy, and this is actually pretty common in stories about Apollo. The guy is simply unlucky in love. You can read more about his bad romances in "Characters: Apollo."