The speaker is trying to talk themselves out of a memory. Over and over they insist that none of it happened: it was a dream, a blink, something only they saw. The short, flat lines and the repeated "Nope" sound like someone slamming a door, though the repetition also suggests they are trying hard to convince themselves.
The last three lines carry the real hurt. The speaker admits they never knew the other person, only the version they believed was them. That is a sharper kind of heartbreak than a simple breakup, because it means the person they loved may never have existed. The title adds to this: throwing out supermarket flowers, cheap and ordinary, hints at a gift or gesture being angrily discarded. The mood is bitter, numb and defensive, with grief sitting just under the denial. The plain wording and the missing apostrophes make it feel raw, like something written quickly in the middle of the feeling.