Lárgate is a strong, informal command meaning "get lost" or "go away." It's more forceful than simply saying "vete" (go).
In this song, the artist uses Lárgate con tus mentiras (Get lost with your lies) to definitively tell a past lover to leave his life, emphasizing his desire for them to disappear completely and take their deceit with them. It perfectly captures the song's theme of moving on from a toxic relationship.
"Fuck Love" is about closing the door on an ex who shows up again expecting to be let back in.
The singer has already grieved, healed, and moved on. When this person comes back after a long silence, he doesn't feel curiosity or hope, just distance: too much time has passed, and it's simply too late for them.
He wants nothing more to do with the relationship. He'd rather be alone than go back to the bad moments and bad company that person brought. Leaving actually gave him peace of mind, and he's not willing to trade that for anything, even while wishing the other person well.
The repeated refusal, "I don't want to go back to your side," is the heart of the song: a clean, final goodbye to someone who thinks they can just walk back in.