Me la rifé is a powerful Mexican slang phrase meaning 'I gave it my all' or 'I went all out'. While the verb rifar literally means 'to raffle', this expression is used to say you risked everything for someone or something.
In the song, Junior H sings, "Si contigo siempre me la rifé" (Since with you, I always gave it my all), to express the deep pain of being betrayed after putting his whole heart on the line. It's a key phrase for understanding the raw, emotional language of modern Regional Mexican music.
This song is a direct and bitter message to an ex. Junior H sings about finding out the truth about his partner, not from her, but from what other people were saying: "Lo que me decía la gente" (What people were telling me). He's in pain and drinking to cope, admitting, "Me trae bien loco la Champán Rose" (The Rosé Champagne is driving me crazy).
Instead of just being sad, he gets angry and sarcastic. He challenges her to keep up her act with her new partner, saying, "Miéntele y úsalo como tú sabes la mente jugar" (Lie to him and use him, since you know how to play mind games). He feels completely betrayed because he gave her his all—"contigo siempre me la rifé" (with you I always gave it my best shot)—and she paid him back badly. He ends with a cold warning and a final goodbye: there's no coming back, and eventually, she's going to end up all by herself. "Que al final sola te vas a quedar" (Because in the end, you'll be left alone).