When we compare someone to a dog, we mean that person has done something bad and caused harm. In this case, the singer is blaming himself, saying that, because he had behaved like a dog with his girlfriend, she broke up with him and is with another man now. Hope it helps!

En esta frase solemos darle el significado de dejadez: "Yo por vago me lo busqué" "Yo por gandul me lo busqué"