Sarra is a popular Mexican slang word that means something is 'lame', 'crappy', or of poor quality. It's an informal but very expressive word that you'll hear in casual conversations.
In the song, the artist laments, "Y neta que sarra tener que mirarla de cerca" (And for real, how crappy to have to see her up close), referring to his ex-girlfriend's mother. The word perfectly captures the awkwardness and frustration of the situation, making it a great piece of authentic slang to learn.
Fuerza Regida brings pure bilingual chaos to this corrido tumbado, kicking things off with a classic vine quote: "I love you bitch, I ain't never going to stop loving you, bitch." From there, the breakup spiral starts. He admits that after getting dumped, he wrecked his life and picked up bad habits: "Traigo el corazón herido, me dejaste bien jodido" [I have a wounded heart, you left me totally screwed]. He even pushed his own friends away ("mandé a la verga a mis amigos") just to focus on her. The English verses mix love and pure spite: "I need ya, I want ya, I love ya, I hate ya." He paid her bills by playing guitar and drove her around in fancy cars, only to end up drinking whiskey alone on freezing nights.
What makes this track stand out is the heavy Mexican street slang. When he says "al chile" [honestly / for real] or "neta que sarra" [honestly it sucks / it is really unpleasant], he is talking straight to you like a homie at a bar. He even mentions running into his ex's mom, who looks at him with pity: "Me cula mi ex-suegra... pero es que no sabe que tú te pasaste de verga" [My ex-mother-in-law likes me... but she just doesn't know that you crossed the line / went way too far]. The idiom "pasarse de verga" is vulgar slang for doing someone dirty or crossing an unforgivable line. It is messy, hilarious, and bitter all at once.