Casé is the past tense of the verb casarse, which means 'to get married'. While you might know this word in the context of a wedding, this song uses it in a deeply poetic and heartbreaking way.
The singer says, "con tu recuerdo yo me casé", which translates to "I married your memory". He uses this powerful metaphor to express that even though he's alone, he is eternally committed to the memory of his past love, making it impossible for him to move on.
In "UNA CERVEZA", US-based group Fuerza Regida and Colombian singer Manuel Turizo team up over a Corrido Tumbado rhythm to confess that getting over an ex is an absolute mess. The narrator hopes that "Una cerveza puede ayudar a que salgas de mi cabeza" ("A beer can help get you out of my head"), but a single drink is clearly not doing the trick. Instead, he is totally derailed. Going out does nothing for him anymore: "Ya no me divierten los amigos y el alcohol" ("Friends and alcohol don't entertain me anymore"), and he is driving around aimlessly while daydreaming about lost plans to buy a house, have kids, and get a dog together.
The track is packed with great everyday Mexican Spanish slang. When he admits that "la neta ya no sé pa' dónde voy" (la neta means "the truth" or "honestly"), he is spelling out just how lost he feels. He even brings up how unfair it is that he woke up next to "una morrita que ni sé cómo se llama" (morrita is slang for "a young woman" or "a girl"), yet he is still stuck thinking about his ex. He boasts that his credit card could not buy the best thing he ever had, admits all his pedas (drinking binges) are dedicated to her, and accepts that winning in life feels useless without her around: "Coronar sin ti es como que fracasé" (coronar, literally "to crown", means to succeed or make it big).