<span>Romeo is discussing how "unnatural" it is that blissful love can make him so miserable.
</span>
Group of stars.
An appositive or appositive phrase renames a noun or pronoun that is right beside, specifically after, it. It is usually used to provide additional information, like a definition or clarification. In this sentence, "group of stars" is defining "constellations" making it the appositive phrase.