Read quickly, "In love" is a tiny story with a sting in its tail. A speaker looks into someone's eye, sees a whole universe, falls in love, and assumes the feeling is shared. Then comes a last sentence that sounds like a compliment and works like a measurement. The central idea lives in the gap between two astronomical words: love is rarely felt at the same size by both people, and the poem lets that mismatch be calculated in space rather than explained in feelings.
The opening image does a lot with very little. "I looked into her eye and i saw the entire universe hiding inside" is built like a zoom, from one small part of a face to everything that exists. "Entire" leaves no room for modesty, which suits infatuation. The verb "hiding" is quietly interesting too. A universe that hides has to be found, so the speaker becomes a discoverer, granted a private view. There is also a pun the poem may or may not intend: "eye" and "I" sound identical, and the sentence uses both. Anyone who has looked closely into another person's eye knows that much of what you see there is your own reflection. The universe the speaker finds may therefore be partly their own hope, projected onto someone else. That is an interpretation, not something the poem states, but the sound-play invites it.
After this expansive sentence the poem drops into plainness. "I was in love." There are four short words, with no imagery and no decoration. Having reached for the cosmos, the speaker names the feeling in the simplest way available, as if the grand image were only a route to a confession. The title repeats the move, and its "In" echoes the "inside" of the first sentence. Love becomes a place you are contained in, just as the universe is contained in the eye.
Nothing rhymes, and in the version we have there are no line breaks, so the poem reads like a few sentences of speech. Its rhythm runs long, short, short, long. The two brief sentences act like held breaths before the final, longer one, and that pacing gives the ending its weight. One small detail deserves a mention: the lowercase "i" in the first sentence, against a capital "I" everywhere else. It may simply be a slip. But it falls exactly where the speaker is dwarfed by the universe, and it is tempting to read it as a shrunken self.
Then the tense turns. "I thought she felt the same." "Thought" is the poem's hinge, because it admits that the belief has already been tested and lost. The whole poem is told from afterwards. Notice, too, the shift from seeing to saying. The speaker saw a universe, but "she said" something about a world. Perception is one kind of evidence and speech is another, and speech can be generous, polite, or less than the whole truth. The poem never accuses her of lying. It just sets what was seen beside what was said and leaves them uncomfortably apart.
The last line, "She said I was her world but she was my galaxy," carries the real argument. "World" is the stock phrase of love songs and greeting cards, warm but earthbound, a single planet. A galaxy holds billions of stars and cannot be crossed. The speaker's "but" shows they hear the imbalance at once. The scale has also slipped: at the start she held a universe, and by the end she is a galaxy. That may be loss, or may be only a change of word, but the direction is downward. A galaxy is also something seen from a great distance, which fits a love that turns out to be unreturned in kind.
What makes the poem worth reading is its restraint. It takes the most worn-out vocabulary of romance (eyes, worlds, the universe) and makes it carry an argument about unequal love without a single complaint. The speaker never says "I was hurt." The reader does the arithmetic of world against galaxy, and that is where the sadness lands. In four sentences, it shows how a cliché can be turned from decoration into evidence.