The speaker looks at love from three distances, each one closer than the last. From the universe's view, people are just tiny particles bouncing around and crashing into each other, with nothing special about it. Then the lens narrows to "the two of us," and the same collisions suddenly feel charged: bodies and eyes become "celestial," "entwined," even "radioactive," a word that suggests both energy and a hint of danger.
The final stanza turns cooler and more honest. The speaker calls the other person an "ersatz soulmate," a placeholder until the real one arrives to end their "cosmic loneliness." It's a surprisingly blunt thing to admit to someone you're close to. The mood mixes wonder with resignation. The speaker enjoys the connection but won't pretend it's permanent, and the lack of a closing full stop leaves the poem feeling unresolved, as if the longing hasn't finished.