The speaker is still hung up on someone who has moved on, and the thing keeping the wound open is a smell. The cologne lingers two weeks later, and what stings most is that the other person wore it for someone else, "for her," while the speaker wishes it had been for them. That one line quietly gives away the whole situation: unreturned feelings, or a love that ended with the speaker on the losing side.
The tone is what makes the poem stand out. The first lines are quiet and hurt, but then the speaker shifts into casual, joking speech: "man," "bro seriously," "what kinda cologne did you bathe in." It sounds like someone trying to laugh off their pain. The admission "I mean yeah I'm still sad and all" is deliberately offhand, as if the sadness is too embarrassing to say straight. The result is a mood that's funny on the surface and aching underneath, where the humor works as a shield that doesn't quite hold.