Suplante comes from the verb suplantar, meaning 'to supplant' or 'to replace'. It's a more powerful and less common word than reemplazar, often implying an illegitimate taking of someone's rightful place.
In the song, Ozuna sings, "No sé si llegará alguien que te suplante" (I don't know if someone will ever come who can replace you). He uses this word to express the profound fear that no one could ever fill the space his lost love occupied, highlighting how unique and irreplaceable she was.
Ozuna kicks off this song by telling us it's a story "Basada en la vida real" [Based on real life], and it feels like one. He's talking about a love that's over, but the memory is so strong it's like a ghost still knocking at the door. He's not trying to be a perfect hero here. He openly admits his flaws, saying "Te he mentido / He pecado igual que tú" [I have lied / I have sinned just like you]. He knows he has a dark side and got carried away by passion.
This all leads to the heartbreaking main idea: "Y se murió el amor" [And the love died]. He compares this lost love to watching a flower die, but not just any flower. It was one "Del único color / Que no creo ver jamás" [Of the only color / that I don't think I'll ever see again]. He's convinced this person was completely unique and irreplaceable. Even as he imagines getting old, he plans to keep their photo under his pillow, and he even asks God to let him keep watching over them after he dies. It's a sad, beautiful song about a love so powerful that its death leaves a permanent mark.