Trigo literally means "wheat". While it might seem strange to call a person this, it's a beautiful and poetic metaphor in this song.
In the lyrics, the singer lists the things his partner is to him: "mi razón, mi paz, mi sol, mi trigo" (my reason, my peace, my sun, my wheat). By comparing her to wheat, a staple food source, he expresses that she is his sustenance and is essential for his survival. It’s a truly unique term of endearment that shows the depth of his love.
This song by Calibre 50 is a pure, heartfelt love letter. The singer is completely in awe of the person he's with, wondering where she's been all his life: "Dime en este tiempo dónde te metiste / Que no te podía encontrar" (Tell me where you were all this time / that I couldn't find you). He doesn't care if it was destiny or God that brought them together; he's just grateful. He adores everything about her, from her positive attitude to her physical imperfections, singing "Amo tus lunares y tus cicatrices" (I love your beauty marks and your scars).
It's a song full of huge promises and declarations. He says he'll be her protector—"para tus miedos yo tengo la cura" (for your fears, I have the cure)—and that she's an answered prayer. The core of the song is in the title: "Simplemente gracias por estar conmigo" (Simply thank you for being with me). It's a direct and sweet expression of gratitude for finding the person who feels like his reason for being, his peace, and his sun. He even throws in a classic, over-the-top romantic line: if there are no stars in the sky, it's because he took them all to give to her.